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+
+<div id="page" class="wide">
+
+
+ <div id="plusone"><g:plusone size="small" annotation="none"></g:plusone></div>
+ <h1>Go 1 Release Notes</h1>
+
+
+
+
+<div id="nav"></div>
+
+
+
+
+<h2 id="introduction">Introduction to Go 1</h2>
+
+<p>
+Go version 1, Go 1 for short, defines a language and a set of core libraries
+that provide a stable foundation for creating reliable products, projects, and
+publications.
+</p>
+
+<p>
+The driving motivation for Go 1 is stability for its users. People should be able to
+write Go programs and expect that they will continue to compile and run without
+change, on a time scale of years, including in production environments such as
+Google App Engine. Similarly, people should be able to write books about Go, be
+able to say which version of Go the book is describing, and have that version
+number still be meaningful much later.
+</p>
+
+<p>
+Code that compiles in Go 1 should, with few exceptions, continue to compile and
+run throughout the lifetime of that version, even as we issue updates and bug
+fixes such as Go version 1.1, 1.2, and so on. Other than critical fixes, changes
+made to the language and library for subsequent releases of Go 1 may
+add functionality but will not break existing Go 1 programs.
+<a href="go1compat.html">The Go 1 compatibility document</a>
+explains the compatibility guidelines in more detail.
+</p>
+
+<p>
+Go 1 is a representation of Go as it used today, not a wholesale rethinking of
+the language. We avoided designing new features and instead focused on cleaning
+up problems and inconsistencies and improving portability. There are a number
+changes to the Go language and packages that we had considered for some time and
+prototyped but not released primarily because they are significant and
+backwards-incompatible. Go 1 was an opportunity to get them out, which is
+helpful for the long term, but also means that Go 1 introduces incompatibilities
+for old programs. Fortunately, the <code>go</code> <code>fix</code> tool can
+automate much of the work needed to bring programs up to the Go 1 standard.
+</p>
+
+<p>
+This document outlines the major changes in Go 1 that will affect programmers
+updating existing code; its reference point is the prior release, r60 (tagged as
+r60.3). It also explains how to update code from r60 to run under Go 1.
+</p>
+
+<h2 id="language">Changes to the language</h2>
+
+<h3 id="append">Append</h3>
+
+<p>
+The <code>append</code> predeclared variadic function makes it easy to grow a slice
+by adding elements to the end.
+A common use is to add bytes to the end of a byte slice when generating output.
+However, <code>append</code> did not provide a way to append a string to a <code>[]byte</code>,
+which is another common case.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/greeting := ..byte/` `/append.*hello/`}}
+--> greeting := []byte{}
+ greeting = append(greeting, []byte(&#34;hello &#34;)...)</pre>
+
+<p>
+By analogy with the similar property of <code>copy</code>, Go 1
+permits a string to be appended (byte-wise) directly to a byte
+slice, reducing the friction between strings and byte slices.
+The conversion is no longer necessary:
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/append.*world/`}}
+--> greeting = append(greeting, &#34;world&#34;...)</pre>
+
+<p>
+<em>Updating</em>:
+This is a new feature, so existing code needs no changes.
+</p>
+
+<h3 id="close">Close</h3>
+
+<p>
+The <code>close</code> predeclared function provides a mechanism
+for a sender to signal that no more values will be sent.
+It is important to the implementation of <code>for</code> <code>range</code>
+loops over channels and is helpful in other situations.
+Partly by design and partly because of race conditions that can occur otherwise,
+it is intended for use only by the goroutine sending on the channel,
+not by the goroutine receiving data.
+However, before Go 1 there was no compile-time checking that <code>close</code>
+was being used correctly.
+</p>
+
+<p>
+To close this gap, at least in part, Go 1 disallows <code>close</code> on receive-only channels.
+Attempting to close such a channel is a compile-time error.
+</p>
+
+<pre>
+ var c chan int
+ var csend chan&lt;- int = c
+ var crecv &lt;-chan int = c
+ close(c) // legal
+ close(csend) // legal
+ close(crecv) // illegal
+</pre>
+
+<p>
+<em>Updating</em>:
+Existing code that attempts to close a receive-only channel was
+erroneous even before Go 1 and should be fixed. The compiler will
+now reject such code.
+</p>
+
+<h3 id="literals">Composite literals</h3>
+
+<p>
+In Go 1, a composite literal of array, slice, or map type can elide the
+type specification for the elements' initializers if they are of pointer type.
+All four of the initializations in this example are legal; the last one was illegal before Go 1.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/type Date struct/` `/STOP/`}}
+--> type Date struct {
+ month string
+ day int
+ }
+ <span class="comment">// Struct values, fully qualified; always legal.</span>
+ holiday1 := []Date{
+ Date{&#34;Feb&#34;, 14},
+ Date{&#34;Nov&#34;, 11},
+ Date{&#34;Dec&#34;, 25},
+ }
+ <span class="comment">// Struct values, type name elided; always legal.</span>
+ holiday2 := []Date{
+ {&#34;Feb&#34;, 14},
+ {&#34;Nov&#34;, 11},
+ {&#34;Dec&#34;, 25},
+ }
+ <span class="comment">// Pointers, fully qualified, always legal.</span>
+ holiday3 := []*Date{
+ &amp;Date{&#34;Feb&#34;, 14},
+ &amp;Date{&#34;Nov&#34;, 11},
+ &amp;Date{&#34;Dec&#34;, 25},
+ }
+ <span class="comment">// Pointers, type name elided; legal in Go 1.</span>
+ holiday4 := []*Date{
+ {&#34;Feb&#34;, 14},
+ {&#34;Nov&#34;, 11},
+ {&#34;Dec&#34;, 25},
+ }</pre>
+
+<p>
+<em>Updating</em>:
+This change has no effect on existing code, but the command
+<code>gofmt</code> <code>-s</code> applied to existing source
+will, among other things, elide explicit element types wherever permitted.
+</p>
+
+
+<h3 id="init">Goroutines during init</h3>
+
+<p>
+The old language defined that <code>go</code> statements executed during initialization created goroutines but that they did not begin to run until initialization of the entire program was complete.
+This introduced clumsiness in many places and, in effect, limited the utility
+of the <code>init</code> construct:
+if it was possible for another package to use the library during initialization, the library
+was forced to avoid goroutines.
+This design was done for reasons of simplicity and safety but,
+as our confidence in the language grew, it seemed unnecessary.
+Running goroutines during initialization is no more complex or unsafe than running them during normal execution.
+</p>
+
+<p>
+In Go 1, code that uses goroutines can be called from
+<code>init</code> routines and global initialization expressions
+without introducing a deadlock.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/PackageGlobal/` `/^}/`}}
+-->var PackageGlobal int
+
+func init() {
+ c := make(chan int)
+ go initializationFunction(c)
+ PackageGlobal = &lt;-c
+}</pre>
+
+<p>
+<em>Updating</em>:
+This is a new feature, so existing code needs no changes,
+although it's possible that code that depends on goroutines not starting before <code>main</code> will break.
+There was no such code in the standard repository.
+</p>
+
+<h3 id="rune">The rune type</h3>
+
+<p>
+The language spec allows the <code>int</code> type to be 32 or 64 bits wide, but current implementations set <code>int</code> to 32 bits even on 64-bit platforms.
+It would be preferable to have <code>int</code> be 64 bits on 64-bit platforms.
+(There are important consequences for indexing large slices.)
+However, this change would waste space when processing Unicode characters with
+the old language because the <code>int</code> type was also used to hold Unicode code points: each code point would waste an extra 32 bits of storage if <code>int</code> grew from 32 bits to 64.
+</p>
+
+<p>
+To make changing to 64-bit <code>int</code> feasible,
+Go 1 introduces a new basic type, <code>rune</code>, to represent
+individual Unicode code points.
+It is an alias for <code>int32</code>, analogous to <code>byte</code>
+as an alias for <code>uint8</code>.
+</p>
+
+<p>
+Character literals such as <code>'a'</code>, <code>'語'</code>, and <code>'\u0345'</code>
+now have default type <code>rune</code>,
+analogous to <code>1.0</code> having default type <code>float64</code>.
+A variable initialized to a character constant will therefore
+have type <code>rune</code> unless otherwise specified.
+</p>
+
+<p>
+Libraries have been updated to use <code>rune</code> rather than <code>int</code>
+when appropriate. For instance, the functions <code>unicode.ToLower</code> and
+relatives now take and return a <code>rune</code>.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/STARTRUNE/` `/ENDRUNE/`}}
+--> delta := &#39;δ&#39; <span class="comment">// delta has type rune.</span>
+ var DELTA rune
+ DELTA = unicode.ToUpper(delta)
+ epsilon := unicode.ToLower(DELTA + 1)
+ if epsilon != &#39;δ&#39;+1 {
+ log.Fatal(&#34;inconsistent casing for Greek&#34;)
+ }</pre>
+
+<p>
+<em>Updating</em>:
+Most source code will be unaffected by this because the type inference from
+<code>:=</code> initializers introduces the new type silently, and it propagates
+from there.
+Some code may get type errors that a trivial conversion will resolve.
+</p>
+
+<h3 id="error">The error type</h3>
+
+<p>
+Go 1 introduces a new built-in type, <code>error</code>, which has the following definition:
+</p>
+
+<pre>
+ type error interface {
+ Error() string
+ }
+</pre>
+
+<p>
+Since the consequences of this type are all in the package library,
+it is discussed <a href="#errors">below</a>.
+</p>
+
+<h3 id="delete">Deleting from maps</h3>
+
+<p>
+In the old language, to delete the entry with key <code>k</code> from map <code>m</code>, one wrote the statement,
+</p>
+
+<pre>
+ m[k] = value, false
+</pre>
+
+<p>
+This syntax was a peculiar special case, the only two-to-one assignment.
+It required passing a value (usually ignored) that is evaluated but discarded,
+plus a boolean that was nearly always the constant <code>false</code>.
+It did the job but was odd and a point of contention.
+</p>
+
+<p>
+In Go 1, that syntax has gone; instead there is a new built-in
+function, <code>delete</code>. The call
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/delete\(m, k\)/`}}
+--> delete(m, k)</pre>
+
+<p>
+will delete the map entry retrieved by the expression <code>m[k]</code>.
+There is no return value. Deleting a non-existent entry is a no-op.
+</p>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will convert expressions of the form <code>m[k] = value,
+false</code> into <code>delete(m, k)</code> when it is clear that
+the ignored value can be safely discarded from the program and
+<code>false</code> refers to the predefined boolean constant.
+The fix tool
+will flag other uses of the syntax for inspection by the programmer.
+</p>
+
+<h3 id="iteration">Iterating in maps</h3>
+
+<p>
+The old language specification did not define the order of iteration for maps,
+and in practice it differed across hardware platforms.
+This caused tests that iterated over maps to be fragile and non-portable, with the
+unpleasant property that a test might always pass on one machine but break on another.
+</p>
+
+<p>
+In Go 1, the order in which elements are visited when iterating
+over a map using a <code>for</code> <code>range</code> statement
+is defined to be unpredictable, even if the same loop is run multiple
+times with the same map.
+Code should not assume that the elements are visited in any particular order.
+</p>
+
+<p>
+This change means that code that depends on iteration order is very likely to break early and be fixed long before it becomes a problem.
+Just as important, it allows the map implementation to ensure better map balancing even when programs are using range loops to select an element from a map.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/Sunday/` `/^ }/`}}
+--> m := map[string]int{&#34;Sunday&#34;: 0, &#34;Monday&#34;: 1}
+ for name, value := range m {
+ <span class="comment">// This loop should not assume Sunday will be visited first.</span>
+ f(name, value)
+ }</pre>
+
+<p>
+<em>Updating</em>:
+This is one change where tools cannot help. Most existing code
+will be unaffected, but some programs may break or misbehave; we
+recommend manual checking of all range statements over maps to
+verify they do not depend on iteration order. There were a few such
+examples in the standard repository; they have been fixed.
+Note that it was already incorrect to depend on the iteration order, which
+was unspecified. This change codifies the unpredictability.
+</p>
+
+<h3 id="multiple_assignment">Multiple assignment</h3>
+
+<p>
+The language specification has long guaranteed that in assignments
+the right-hand-side expressions are all evaluated before any left-hand-side expressions are assigned.
+To guarantee predictable behavior,
+Go 1 refines the specification further.
+</p>
+
+<p>
+If the left-hand side of the assignment
+statement contains expressions that require evaluation, such as
+function calls or array indexing operations, these will all be done
+using the usual left-to-right rule before any variables are assigned
+their value. Once everything is evaluated, the actual assignments
+proceed in left-to-right order.
+</p>
+
+<p>
+These examples illustrate the behavior.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/sa :=/` `/then sc.0. = 2/`}}
+--> sa := []int{1, 2, 3}
+ i := 0
+ i, sa[i] = 1, 2 <span class="comment">// sets i = 1, sa[0] = 2</span>
+
+ sb := []int{1, 2, 3}
+ j := 0
+ sb[j], j = 2, 1 <span class="comment">// sets sb[0] = 2, j = 1</span>
+
+ sc := []int{1, 2, 3}
+ sc[0], sc[0] = 1, 2 <span class="comment">// sets sc[0] = 1, then sc[0] = 2 (so sc[0] = 2 at end)</span></pre>
+
+<p>
+<em>Updating</em>:
+This is one change where tools cannot help, but breakage is unlikely.
+No code in the standard repository was broken by this change, and code
+that depended on the previous unspecified behavior was already incorrect.
+</p>
+
+<h3 id="shadowing">Returns and shadowed variables</h3>
+
+<p>
+A common mistake is to use <code>return</code> (without arguments) after an assignment to a variable that has the same name as a result variable but is not the same variable.
+This situation is called <em>shadowing</em>: the result variable has been shadowed by another variable with the same name declared in an inner scope.
+</p>
+
+<p>
+In functions with named return values,
+the Go 1 compilers disallow return statements without arguments if any of the named return values is shadowed at the point of the return statement.
+(It isn't part of the specification, because this is one area we are still exploring;
+the situation is analogous to the compilers rejecting functions that do not end with an explicit return statement.)
+</p>
+
+<p>
+This function implicitly returns a shadowed return value and will be rejected by the compiler:
+</p>
+
+<pre>
+ func Bug() (i, j, k int) {
+ for i = 0; i &lt; 5; i++ {
+ for j := 0; j &lt; 5; j++ { // Redeclares j.
+ k += i*j
+ if k > 100 {
+ return // Rejected: j is shadowed here.
+ }
+ }
+ }
+ return // OK: j is not shadowed here.
+ }
+</pre>
+
+<p>
+<em>Updating</em>:
+Code that shadows return values in this way will be rejected by the compiler and will need to be fixed by hand.
+The few cases that arose in the standard repository were mostly bugs.
+</p>
+
+<h3 id="unexported">Copying structs with unexported fields</h3>
+
+<p>
+The old language did not allow a package to make a copy of a struct value containing unexported fields belonging to a different package.
+There was, however, a required exception for a method receiver;
+also, the implementations of <code>copy</code> and <code>append</code> have never honored the restriction.
+</p>
+
+<p>
+Go 1 will allow packages to copy struct values containing unexported fields from other packages.
+Besides resolving the inconsistency,
+this change admits a new kind of API: a package can return an opaque value without resorting to a pointer or interface.
+The new implementations of <code>time.Time</code> and
+<code>reflect.Value</code> are examples of types taking advantage of this new property.
+</p>
+
+<p>
+As an example, if package <code>p</code> includes the definitions,
+</p>
+
+<pre>
+ type Struct struct {
+ Public int
+ secret int
+ }
+ func NewStruct(a int) Struct { // Note: not a pointer.
+ return Struct{a, f(a)}
+ }
+ func (s Struct) String() string {
+ return fmt.Sprintf("{%d (secret %d)}", s.Public, s.secret)
+ }
+</pre>
+
+<p>
+a package that imports <code>p</code> can assign and copy values of type
+<code>p.Struct</code> at will.
+Behind the scenes the unexported fields will be assigned and copied just
+as if they were exported,
+but the client code will never be aware of them. The code
+</p>
+
+<pre>
+ import "p"
+
+ myStruct := p.NewStruct(23)
+ copyOfMyStruct := myStruct
+ fmt.Println(myStruct, copyOfMyStruct)
+</pre>
+
+<p>
+will show that the secret field of the struct has been copied to the new value.
+</p>
+
+<p>
+<em>Updating</em>:
+This is a new feature, so existing code needs no changes.
+</p>
+
+<h3 id="equality">Equality</h3>
+
+<p>
+Before Go 1, the language did not define equality on struct and array values.
+This meant,
+among other things, that structs and arrays could not be used as map keys.
+On the other hand, Go did define equality on function and map values.
+Function equality was problematic in the presence of closures
+(when are two closures equal?)
+while map equality compared pointers, not the maps' content, which was usually
+not what the user would want.
+</p>
+
+<p>
+Go 1 addressed these issues.
+First, structs and arrays can be compared for equality and inequality
+(<code>==</code> and <code>!=</code>),
+and therefore be used as map keys,
+provided they are composed from elements for which equality is also defined,
+using element-wise comparison.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/type Day struct/` `/Printf/`}}
+--> type Day struct {
+ long string
+ short string
+ }
+ Christmas := Day{&#34;Christmas&#34;, &#34;XMas&#34;}
+ Thanksgiving := Day{&#34;Thanksgiving&#34;, &#34;Turkey&#34;}
+ holiday := map[Day]bool{
+ Christmas: true,
+ Thanksgiving: true,
+ }
+ fmt.Printf(&#34;Christmas is a holiday: %t\n&#34;, holiday[Christmas])</pre>
+
+<p>
+Second, Go 1 removes the definition of equality for function values,
+except for comparison with <code>nil</code>.
+Finally, map equality is gone too, also except for comparison with <code>nil</code>.
+</p>
+
+<p>
+Note that equality is still undefined for slices, for which the
+calculation is in general infeasible. Also note that the ordered
+comparison operators (<code>&lt;</code> <code>&lt;=</code>
+<code>&gt;</code> <code>&gt;=</code>) are still undefined for
+structs and arrays.
+
+<p>
+<em>Updating</em>:
+Struct and array equality is a new feature, so existing code needs no changes.
+Existing code that depends on function or map equality will be
+rejected by the compiler and will need to be fixed by hand.
+Few programs will be affected, but the fix may require some
+redesign.
+</p>
+
+<h2 id="packages">The package hierarchy</h2>
+
+<p>
+Go 1 addresses many deficiencies in the old standard library and
+cleans up a number of packages, making them more internally consistent
+and portable.
+</p>
+
+<p>
+This section describes how the packages have been rearranged in Go 1.
+Some have moved, some have been renamed, some have been deleted.
+New packages are described in later sections.
+</p>
+
+<h3 id="hierarchy">The package hierarchy</h3>
+
+<p>
+Go 1 has a rearranged package hierarchy that groups related items
+into subdirectories. For instance, <code>utf8</code> and
+<code>utf16</code> now occupy subdirectories of <code>unicode</code>.
+Also, <a href="#subrepo">some packages</a> have moved into
+subrepositories of
+<a href="http://code.google.com/p/go"><code>code.google.com/p/go</code></a>
+while <a href="#deleted">others</a> have been deleted outright.
+</p>
+
+<table class="codetable" frame="border" summary="Moved packages">
+<colgroup align="left" width="60%"></colgroup>
+<colgroup align="left" width="40%"></colgroup>
+<tr>
+<th align="left">Old path</th>
+<th align="left">New path</th>
+</tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>asn1</td> <td>encoding/asn1</td></tr>
+<tr><td>csv</td> <td>encoding/csv</td></tr>
+<tr><td>gob</td> <td>encoding/gob</td></tr>
+<tr><td>json</td> <td>encoding/json</td></tr>
+<tr><td>xml</td> <td>encoding/xml</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>exp/template/html</td> <td>html/template</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>big</td> <td>math/big</td></tr>
+<tr><td>cmath</td> <td>math/cmplx</td></tr>
+<tr><td>rand</td> <td>math/rand</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>http</td> <td>net/http</td></tr>
+<tr><td>http/cgi</td> <td>net/http/cgi</td></tr>
+<tr><td>http/fcgi</td> <td>net/http/fcgi</td></tr>
+<tr><td>http/httptest</td> <td>net/http/httptest</td></tr>
+<tr><td>http/pprof</td> <td>net/http/pprof</td></tr>
+<tr><td>mail</td> <td>net/mail</td></tr>
+<tr><td>rpc</td> <td>net/rpc</td></tr>
+<tr><td>rpc/jsonrpc</td> <td>net/rpc/jsonrpc</td></tr>
+<tr><td>smtp</td> <td>net/smtp</td></tr>
+<tr><td>url</td> <td>net/url</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>exec</td> <td>os/exec</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>scanner</td> <td>text/scanner</td></tr>
+<tr><td>tabwriter</td> <td>text/tabwriter</td></tr>
+<tr><td>template</td> <td>text/template</td></tr>
+<tr><td>template/parse</td> <td>text/template/parse</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>utf8</td> <td>unicode/utf8</td></tr>
+<tr><td>utf16</td> <td>unicode/utf16</td></tr>
+</table>
+
+<p>
+Note that the package names for the old <code>cmath</code> and
+<code>exp/template/html</code> packages have changed to <code>cmplx</code>
+and <code>template</code>.
+</p>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will update all imports and package renames for packages that
+remain inside the standard repository. Programs that import packages
+that are no longer in the standard repository will need to be edited
+by hand.
+</p>
+
+<h3 id="exp">The package tree exp</h3>
+
+<p>
+Because they are not standardized, the packages under the <code>exp</code> directory will not be available in the
+standard Go 1 release distributions, although they will be available in source code form
+in <a href="http://code.google.com/p/go/">the repository</a> for
+developers who wish to use them.
+</p>
+
+<p>
+Several packages have moved under <code>exp</code> at the time of Go 1's release:
+</p>
+
+<ul>
+<li><code>ebnf</code></li>
+<li><code>html</code><sup>&#8224;</sup></li>
+<li><code>go/types</code></li>
+</ul>
+
+<p>
+(<sup>&#8224;</sup>The <code>EscapeString</code> and <code>UnescapeString</code> types remain
+in package <code>html</code>.)
+</p>
+
+<p>
+All these packages are available under the same names, with the prefix <code>exp/</code>: <code>exp/ebnf</code> etc.
+</p>
+
+<p>
+Also, the <code>utf8.String</code> type has been moved to its own package, <code>exp/utf8string</code>.
+</p>
+
+<p>
+Finally, the <code>gotype</code> command now resides in <code>exp/gotype</code>, while
+<code>ebnflint</code> is now in <code>exp/ebnflint</code>.
+If they are installed, they now reside in <code>$GOROOT/bin/tool</code>.
+</p>
+
+<p>
+<em>Updating</em>:
+Code that uses packages in <code>exp</code> will need to be updated by hand,
+or else compiled from an installation that has <code>exp</code> available.
+The <code>go</code> <code>fix</code> tool or the compiler will complain about such uses.
+</p>
+
+<h3 id="old">The package tree old</h3>
+
+<p>
+Because they are deprecated, the packages under the <code>old</code> directory will not be available in the
+standard Go 1 release distributions, although they will be available in source code form for
+developers who wish to use them.
+</p>
+
+<p>
+The packages in their new locations are:
+</p>
+
+<ul>
+<li><code>old/netchan</code></li>
+<li><code>old/regexp</code></li>
+<li><code>old/template</code></li>
+</ul>
+
+<p>
+<em>Updating</em>:
+Code that uses packages now in <code>old</code> will need to be updated by hand,
+or else compiled from an installation that has <code>old</code> available.
+The <code>go</code> <code>fix</code> tool will warn about such uses.
+</p>
+
+<h3 id="deleted">Deleted packages</h3>
+
+<p>
+Go 1 deletes several packages outright:
+</p>
+
+<ul>
+<li><code>container/vector</code></li>
+<li><code>exp/datafmt</code></li>
+<li><code>go/typechecker</code></li>
+<li><code>try</code></li>
+</ul>
+
+<p>
+and also the command <code>gotry</code>.
+</p>
+
+<p>
+<em>Updating</em>:
+Code that uses <code>container/vector</code> should be updated to use
+slices directly. See
+<a href="http://code.google.com/p/go-wiki/wiki/SliceTricks">the Go
+Language Community Wiki</a> for some suggestions.
+Code that uses the other packages (there should be almost zero) will need to be rethought.
+</p>
+
+<h3 id="subrepo">Packages moving to subrepositories</h3>
+
+<p>
+Go 1 has moved a number of packages into other repositories, usually sub-repositories of
+<a href="http://code.google.com/p/go/">the main Go repository</a>.
+This table lists the old and new import paths:
+
+<table class="codetable" frame="border" summary="Sub-repositories">
+<colgroup align="left" width="40%"></colgroup>
+<colgroup align="left" width="60%"></colgroup>
+<tr>
+<th align="left">Old</th>
+<th align="left">New</th>
+</tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>crypto/bcrypt</td> <td>code.google.com/p/go.crypto/bcrypt</tr>
+<tr><td>crypto/blowfish</td> <td>code.google.com/p/go.crypto/blowfish</tr>
+<tr><td>crypto/cast5</td> <td>code.google.com/p/go.crypto/cast5</tr>
+<tr><td>crypto/md4</td> <td>code.google.com/p/go.crypto/md4</tr>
+<tr><td>crypto/ocsp</td> <td>code.google.com/p/go.crypto/ocsp</tr>
+<tr><td>crypto/openpgp</td> <td>code.google.com/p/go.crypto/openpgp</tr>
+<tr><td>crypto/openpgp/armor</td> <td>code.google.com/p/go.crypto/openpgp/armor</tr>
+<tr><td>crypto/openpgp/elgamal</td> <td>code.google.com/p/go.crypto/openpgp/elgamal</tr>
+<tr><td>crypto/openpgp/errors</td> <td>code.google.com/p/go.crypto/openpgp/errors</tr>
+<tr><td>crypto/openpgp/packet</td> <td>code.google.com/p/go.crypto/openpgp/packet</tr>
+<tr><td>crypto/openpgp/s2k</td> <td>code.google.com/p/go.crypto/openpgp/s2k</tr>
+<tr><td>crypto/ripemd160</td> <td>code.google.com/p/go.crypto/ripemd160</tr>
+<tr><td>crypto/twofish</td> <td>code.google.com/p/go.crypto/twofish</tr>
+<tr><td>crypto/xtea</td> <td>code.google.com/p/go.crypto/xtea</tr>
+<tr><td>exp/ssh</td> <td>code.google.com/p/go.crypto/ssh</tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>image/bmp</td> <td>code.google.com/p/go.image/bmp</tr>
+<tr><td>image/tiff</td> <td>code.google.com/p/go.image/tiff</tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>net/dict</td> <td>code.google.com/p/go.net/dict</tr>
+<tr><td>net/websocket</td> <td>code.google.com/p/go.net/websocket</tr>
+<tr><td>exp/spdy</td> <td>code.google.com/p/go.net/spdy</tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>encoding/git85</td> <td>code.google.com/p/go.codereview/git85</tr>
+<tr><td>patch</td> <td>code.google.com/p/go.codereview/patch</tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>exp/wingui</td> <td>code.google.com/p/gowingui</tr>
+</table>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will update imports of these packages to use the new import paths.
+Installations that depend on these packages will need to install them using
+a <code>go get</code> command.
+</p>
+
+<h2 id="major">Major changes to the library</h2>
+
+<p>
+This section describes significant changes to the core libraries, the ones that
+affect the most programs.
+</p>
+
+<h3 id="errors">The error type and errors package</h3>
+
+<p>
+The placement of <code>os.Error</code> in package <code>os</code> is mostly historical: errors first came up when implementing package <code>os</code>, and they seemed system-related at the time.
+Since then it has become clear that errors are more fundamental than the operating system. For example, it would be nice to use <code>Errors</code> in packages that <code>os</code> depends on, like <code>syscall</code>.
+Also, having <code>Error</code> in <code>os</code> introduces many dependencies on <code>os</code> that would otherwise not exist.
+</p>
+
+<p>
+Go 1 solves these problems by introducing a built-in <code>error</code> interface type and a separate <code>errors</code> package (analogous to <code>bytes</code> and <code>strings</code>) that contains utility functions.
+It replaces <code>os.NewError</code> with
+<a href="/pkg/errors/#New"><code>errors.New</code></a>,
+giving errors a more central place in the environment.
+</p>
+
+<p>
+So the widely-used <code>String</code> method does not cause accidental satisfaction
+of the <code>error</code> interface, the <code>error</code> interface uses instead
+the name <code>Error</code> for that method:
+</p>
+
+<pre>
+ type error interface {
+ Error() string
+ }
+</pre>
+
+<p>
+The <code>fmt</code> library automatically invokes <code>Error</code>, as it already
+does for <code>String</code>, for easy printing of error values.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/START ERROR EXAMPLE/` `/END ERROR EXAMPLE/`}}
+-->type SyntaxError struct {
+ File string
+ Line int
+ Message string
+}
+
+func (se *SyntaxError) Error() string {
+ return fmt.Sprintf(&#34;%s:%d: %s&#34;, se.File, se.Line, se.Message)
+}</pre>
+
+<p>
+All standard packages have been updated to use the new interface; the old <code>os.Error</code> is gone.
+</p>
+
+<p>
+A new package, <a href="/pkg/errors/"><code>errors</code></a>, contains the function
+</p>
+
+<pre>
+func New(text string) error
+</pre>
+
+<p>
+to turn a string into an error. It replaces the old <code>os.NewError</code>.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/ErrSyntax/`}}
+--> var ErrSyntax = errors.New(&#34;syntax error&#34;)</pre>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will update almost all code affected by the change.
+Code that defines error types with a <code>String</code> method will need to be updated
+by hand to rename the methods to <code>Error</code>.
+</p>
+
+<h3 id="errno">System call errors</h3>
+
+<p>
+The old <code>syscall</code> package, which predated <code>os.Error</code>
+(and just about everything else),
+returned errors as <code>int</code> values.
+In turn, the <code>os</code> package forwarded many of these errors, such
+as <code>EINVAL</code>, but using a different set of errors on each platform.
+This behavior was unpleasant and unportable.
+</p>
+
+<p>
+In Go 1, the
+<a href="/pkg/syscall/"><code>syscall</code></a>
+package instead returns an <code>error</code> for system call errors.
+On Unix, the implementation is done by a
+<a href="/pkg/syscall/#Errno"><code>syscall.Errno</code></a> type
+that satisfies <code>error</code> and replaces the old <code>os.Errno</code>.
+</p>
+
+<p>
+The changes affecting <code>os.EINVAL</code> and relatives are
+described <a href="#os">elsewhere</a>.
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will update almost all code affected by the change.
+Regardless, most code should use the <code>os</code> package
+rather than <code>syscall</code> and so will be unaffected.
+</p>
+
+<h3 id="time">Time</h3>
+
+<p>
+Time is always a challenge to support well in a programming language.
+The old Go <code>time</code> package had <code>int64</code> units, no
+real type safety,
+and no distinction between absolute times and durations.
+</p>
+
+<p>
+One of the most sweeping changes in the Go 1 library is therefore a
+complete redesign of the
+<a href="/pkg/time/"><code>time</code></a> package.
+Instead of an integer number of nanoseconds as an <code>int64</code>,
+and a separate <code>*time.Time</code> type to deal with human
+units such as hours and years,
+there are now two fundamental types:
+<a href="/pkg/time/#Time"><code>time.Time</code></a>
+(a value, so the <code>*</code> is gone), which represents a moment in time;
+and <a href="/pkg/time/#Duration"><code>time.Duration</code></a>,
+which represents an interval.
+Both have nanosecond resolution.
+A <code>Time</code> can represent any time into the ancient
+past and remote future, while a <code>Duration</code> can
+span plus or minus only about 290 years.
+There are methods on these types, plus a number of helpful
+predefined constant durations such as <code>time.Second</code>.
+</p>
+
+<p>
+Among the new methods are things like
+<a href="/pkg/time/#Time.Add"><code>Time.Add</code></a>,
+which adds a <code>Duration</code> to a <code>Time</code>, and
+<a href="/pkg/time/#Time.Sub"><code>Time.Sub</code></a>,
+which subtracts two <code>Times</code> to yield a <code>Duration</code>.
+</p>
+
+<p>
+The most important semantic change is that the Unix epoch (Jan 1, 1970) is now
+relevant only for those functions and methods that mention Unix:
+<a href="/pkg/time/#Unix"><code>time.Unix</code></a>
+and the <a href="/pkg/time/#Time.Unix"><code>Unix</code></a>
+and <a href="/pkg/time/#Time.UnixNano"><code>UnixNano</code></a> methods
+of the <code>Time</code> type.
+In particular,
+<a href="/pkg/time/#Now"><code>time.Now</code></a>
+returns a <code>time.Time</code> value rather than, in the old
+API, an integer nanosecond count since the Unix epoch.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/sleepUntil/` `/^}/`}}
+--><span class="comment">// sleepUntil sleeps until the specified time. It returns immediately if it&#39;s too late.</span>
+func sleepUntil(wakeup time.Time) {
+ now := time.Now() <span class="comment">// A Time.</span>
+ if !wakeup.After(now) {
+ return
+ }
+ delta := wakeup.Sub(now) <span class="comment">// A Duration.</span>
+ fmt.Printf(&#34;Sleeping for %.3fs\n&#34;, delta.Seconds())
+ time.Sleep(delta)
+}</pre>
+
+<p>
+The new types, methods, and constants have been propagated through
+all the standard packages that use time, such as <code>os</code> and
+its representation of file time stamps.
+</p>
+
+<p>
+<em>Updating</em>:
+The <code>go</code> <code>fix</code> tool will update many uses of the old <code>time</code> package to use the new
+types and methods, although it does not replace values such as <code>1e9</code>
+representing nanoseconds per second.
+Also, because of type changes in some of the values that arise,
+some of the expressions rewritten by the fix tool may require
+further hand editing; in such cases the rewrite will include
+the correct function or method for the old functionality, but
+may have the wrong type or require further analysis.
+</p>
+
+<h2 id="minor">Minor changes to the library</h2>
+
+<p>
+This section describes smaller changes, such as those to less commonly
+used packages or that affect
+few programs beyond the need to run <code>go</code> <code>fix</code>.
+This category includes packages that are new in Go 1.
+Collectively they improve portability, regularize behavior, and
+make the interfaces more modern and Go-like.
+</p>
+
+<h3 id="archive_zip">The archive/zip package</h3>
+
+<p>
+In Go 1, <a href="/pkg/archive/zip/#Writer"><code>*zip.Writer</code></a> no
+longer has a <code>Write</code> method. Its presence was a mistake.
+</p>
+
+<p>
+<em>Updating</em>:
+What little code is affected will be caught by the compiler and must be updated by hand.
+</p>
+
+<h3 id="bufio">The bufio package</h3>
+
+<p>
+In Go 1, <a href="/pkg/bufio/#NewReaderSize"><code>bufio.NewReaderSize</code></a>
+and
+<a href="/pkg/bufio/#NewWriterSize"><code>bufio.NewWriterSize</code></a>
+functions no longer return an error for invalid sizes.
+If the argument size is too small or invalid, it is adjusted.
+</p>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will update calls that assign the error to _.
+Calls that aren't fixed will be caught by the compiler and must be updated by hand.
+</p>
+
+<h3 id="compress">The compress/flate, compress/gzip and compress/zlib packages</h3>
+
+<p>
+In Go 1, the <code>NewWriterXxx</code> functions in
+<a href="/pkg/compress/flate"><code>compress/flate</code></a>,
+<a href="/pkg/compress/gzip"><code>compress/gzip</code></a> and
+<a href="/pkg/compress/zlib"><code>compress/zlib</code></a>
+all return <code>(*Writer, error)</code> if they take a compression level,
+and <code>*Writer</code> otherwise. Package <code>gzip</code>'s
+<code>Compressor</code> and <code>Decompressor</code> types have been renamed
+to <code>Writer</code> and <code>Reader</code>. Package <code>flate</code>'s
+<code>WrongValueError</code> type has been removed.
+</p>
+
+<p>
+<em>Updating</em>
+Running <code>go</code> <code>fix</code> will update old names and calls that assign the error to _.
+Calls that aren't fixed will be caught by the compiler and must be updated by hand.
+</p>
+
+<h3 id="crypto_aes_des">The crypto/aes and crypto/des packages</h3>
+
+<p>
+In Go 1, the <code>Reset</code> method has been removed. Go does not guarantee
+that memory is not copied and therefore this method was misleading.
+</p>
+
+<p>
+The cipher-specific types <code>*aes.Cipher</code>, <code>*des.Cipher</code>,
+and <code>*des.TripleDESCipher</code> have been removed in favor of
+<code>cipher.Block</code>.
+</p>
+
+<p>
+<em>Updating</em>:
+Remove the calls to Reset. Replace uses of the specific cipher types with
+cipher.Block.
+</p>
+
+<h3 id="crypto_elliptic">The crypto/elliptic package</h3>
+
+<p>
+In Go 1, <a href="/pkg/crypto/elliptic/#Curve"><code>elliptic.Curve</code></a>
+has been made an interface to permit alternative implementations. The curve
+parameters have been moved to the
+<a href="/pkg/crypto/elliptic/#CurveParams"><code>elliptic.CurveParams</code></a>
+structure.
+</p>
+
+<p>
+<em>Updating</em>:
+Existing users of <code>*elliptic.Curve</code> will need to change to
+simply <code>elliptic.Curve</code>. Calls to <code>Marshal</code>,
+<code>Unmarshal</code> and <code>GenerateKey</code> are now functions
+in <code>crypto/elliptic</code> that take an <code>elliptic.Curve</code>
+as their first argument.
+</p>
+
+<h3 id="crypto_hmac">The crypto/hmac package</h3>
+
+<p>
+In Go 1, the hash-specific functions, such as <code>hmac.NewMD5</code>, have
+been removed from <code>crypto/hmac</code>. Instead, <code>hmac.New</code> takes
+a function that returns a <code>hash.Hash</code>, such as <code>md5.New</code>.
+</p>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will perform the needed changes.
+</p>
+
+<h3 id="crypto_x509">The crypto/x509 package</h3>
+
+<p>
+In Go 1, the
+<a href="/pkg/crypto/x509/#CreateCertificate"><code>CreateCertificate</code></a>
+and
+<a href="/pkg/crypto/x509/#CreateCRL"><code>CreateCRL</code></a>
+functions in <code>crypto/x509</code> have been altered to take an
+<code>interface{}</code> where they previously took a <code>*rsa.PublicKey</code>
+or <code>*rsa.PrivateKey</code>. This will allow other public key algorithms
+to be implemented in the future.
+</p>
+
+<p>
+<em>Updating</em>:
+No changes will be needed.
+</p>
+
+<h3 id="encoding_binary">The encoding/binary package</h3>
+
+<p>
+In Go 1, the <code>binary.TotalSize</code> function has been replaced by
+<a href="/pkg/encoding/binary/#Size"><code>Size</code></a>,
+which takes an <code>interface{}</code> argument rather than
+a <code>reflect.Value</code>.
+</p>
+
+<p>
+<em>Updating</em>:
+What little code is affected will be caught by the compiler and must be updated by hand.
+</p>
+
+<h3 id="encoding_xml">The encoding/xml package</h3>
+
+<p>
+In Go 1, the <a href="/pkg/encoding/xml/"><code>xml</code></a> package
+has been brought closer in design to the other marshaling packages such
+as <a href="/pkg/encoding/gob/"><code>encoding/gob</code></a>.
+</p>
+
+<p>
+The old <code>Parser</code> type is renamed
+<a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> and has a new
+<a href="/pkg/encoding/xml/#Decoder.Decode"><code>Decode</code></a> method. An
+<a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a> type was also introduced.
+</p>
+
+<p>
+The functions <a href="/pkg/encoding/xml/#Marshal"><code>Marshal</code></a>
+and <a href="/pkg/encoding/xml/#Unmarshal"><code>Unmarshal</code></a>
+work with <code>[]byte</code> values now. To work with streams,
+use the new <a href="/pkg/encoding/xml/#Encoder"><code>Encoder</code></a>
+and <a href="/pkg/encoding/xml/#Decoder"><code>Decoder</code></a> types.
+</p>
+
+<p>
+When marshaling or unmarshaling values, the format of supported flags in
+field tags has changed to be closer to the
+<a href="/pkg/encoding/json"><code>json</code></a> package
+(<code>`xml:"name,flag"`</code>). The matching done between field tags, field
+names, and the XML attribute and element names is now case-sensitive.
+The <code>XMLName</code> field tag, if present, must also match the name
+of the XML element being marshaled.
+</p>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will update most uses of the package except for some calls to
+<code>Unmarshal</code>. Special care must be taken with field tags,
+since the fix tool will not update them and if not fixed by hand they will
+misbehave silently in some cases. For example, the old
+<code>"attr"</code> is now written <code>",attr"</code> while plain
+<code>"attr"</code> remains valid but with a different meaning.
+</p>
+
+<h3 id="expvar">The expvar package</h3>
+
+<p>
+In Go 1, the <code>RemoveAll</code> function has been removed.
+The <code>Iter</code> function and Iter method on <code>*Map</code> have
+been replaced by
+<a href="/pkg/expvar/#Do"><code>Do</code></a>
+and
+<a href="/pkg/expvar/#Map.Do"><code>(*Map).Do</code></a>.
+</p>
+
+<p>
+<em>Updating</em>:
+Most code using <code>expvar</code> will not need changing. The rare code that used
+<code>Iter</code> can be updated to pass a closure to <code>Do</code> to achieve the same effect.
+</p>
+
+<h3 id="flag">The flag package</h3>
+
+<p>
+In Go 1, the interface <a href="/pkg/flag/#Value"><code>flag.Value</code></a> has changed slightly.
+The <code>Set</code> method now returns an <code>error</code> instead of
+a <code>bool</code> to indicate success or failure.
+</p>
+
+<p>
+There is also a new kind of flag, <code>Duration</code>, to support argument
+values specifying time intervals.
+Values for such flags must be given units, just as <code>time.Duration</code>
+formats them: <code>10s</code>, <code>1h30m</code>, etc.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/timeout/`}}
+-->var timeout = flag.Duration(&#34;timeout&#34;, 30*time.Second, &#34;how long to wait for completion&#34;)</pre>
+
+<p>
+<em>Updating</em>:
+Programs that implement their own flags will need minor manual fixes to update their
+<code>Set</code> methods.
+The <code>Duration</code> flag is new and affects no existing code.
+</p>
+
+
+<h3 id="go">The go/* packages</h3>
+
+<p>
+Several packages under <code>go</code> have slightly revised APIs.
+</p>
+
+<p>
+A concrete <code>Mode</code> type was introduced for configuration mode flags
+in the packages
+<a href="/pkg/go/scanner/"><code>go/scanner</code></a>,
+<a href="/pkg/go/parser/"><code>go/parser</code></a>,
+<a href="/pkg/go/printer/"><code>go/printer</code></a>, and
+<a href="/pkg/go/doc/"><code>go/doc</code></a>.
+</p>
+
+<p>
+The modes <code>AllowIllegalChars</code> and <code>InsertSemis</code> have been removed
+from the <a href="/pkg/go/scanner/"><code>go/scanner</code></a> package. They were mostly
+useful for scanning text other then Go source files. Instead, the
+<a href="/pkg/text/scanner/"><code>text/scanner</code></a> package should be used
+for that purpose.
+</p>
+
+<p>
+The <a href="/pkg/go/scanner/#ErrorHandler"><code>ErrorHandler</code></a> provided
+to the scanner's <a href="/pkg/go/scanner/#Scanner.Init"><code>Init</code></a> method is
+now simply a function rather than an interface. The <code>ErrorVector</code> type has
+been removed in favor of the (existing) <a href="/pkg/go/scanner/#ErrorList"><code>ErrorList</code></a>
+type, and the <code>ErrorVector</code> methods have been migrated. Instead of embedding
+an <code>ErrorVector</code> in a client of the scanner, now a client should maintain
+an <code>ErrorList</code>.
+</p>
+
+<p>
+The set of parse functions provided by the <a href="/pkg/go/parser/"><code>go/parser</code></a>
+package has been reduced to the primary parse function
+<a href="/pkg/go/parser/#ParseFile"><code>ParseFile</code></a>, and a couple of
+convenience functions <a href="/pkg/go/parser/#ParseDir"><code>ParseDir</code></a>
+and <a href="/pkg/go/parser/#ParseExpr"><code>ParseExpr</code></a>.
+</p>
+
+<p>
+The <a href="/pkg/go/printer/"><code>go/printer</code></a> package supports an additional
+configuration mode <a href="/pkg/go/printer/#Mode"><code>SourcePos</code></a>;
+if set, the printer will emit <code>//line</code> comments such that the generated
+output contains the original source code position information. The new type
+<a href="/pkg/go/printer/#CommentedNode"><code>CommentedNode</code></a> can be
+used to provide comments associated with an arbitrary
+<a href="/pkg/go/ast/#Node"><code>ast.Node</code></a> (until now only
+<a href="/pkg/go/ast/#File"><code>ast.File</code></a> carried comment information).
+</p>
+
+<p>
+The type names of the <a href="/pkg/go/doc/"><code>go/doc</code></a> package have been
+streamlined by removing the <code>Doc</code> suffix: <code>PackageDoc</code>
+is now <code>Package</code>, <code>ValueDoc</code> is <code>Value</code>, etc.
+Also, all types now consistently have a <code>Name</code> field (or <code>Names</code>,
+in the case of type <code>Value</code>) and <code>Type.Factories</code> has become
+<code>Type.Funcs</code>.
+Instead of calling <code>doc.NewPackageDoc(pkg, importpath)</code>,
+documentation for a package is created with:
+</p>
+
+<pre>
+ doc.New(pkg, importpath, mode)
+</pre>
+
+<p>
+where the new <code>mode</code> parameter specifies the operation mode:
+if set to <a href="/pkg/go/doc/#AllDecls"><code>AllDecls</code></a>, all declarations
+(not just exported ones) are considered.
+The function <code>NewFileDoc</code> was removed, and the function
+<code>CommentText</code> has become the method
+<a href="/pkg/go/ast/#Text"><code>Text</code></a> of
+<a href="/pkg/go/ast/#CommentGroup"><code>ast.CommentGroup</code></a>.
+</p>
+
+<p>
+In package <a href="/pkg/go/token/"><code>go/token</code></a>, the
+<a href="/pkg/go/token/#FileSet"><code>token.FileSet</code></a> method <code>Files</code>
+(which originally returned a channel of <code>*token.File</code>s) has been replaced
+with the iterator <a href="/pkg/go/token/#FileSet.Iterate"><code>Iterate</code></a> that
+accepts a function argument instead.
+</p>
+
+<p>
+In package <a href="/pkg/go/build/"><code>go/build</code></a>, the API
+has been nearly completely replaced.
+The package still computes Go package information
+but it does not run the build: the <code>Cmd</code> and <code>Script</code>
+types are gone.
+(To build code, use the new
+<a href="/cmd/go/"><code>go</code></a> command instead.)
+The <code>DirInfo</code> type is now named
+<a href="/pkg/go/build/#Package"><code>Package</code></a>.
+<code>FindTree</code> and <code>ScanDir</code> are replaced by
+<a href="/pkg/go/build/#Import"><code>Import</code></a>
+and
+<a href="/pkg/go/build/#ImportDir"><code>ImportDir</code></a>.
+</p>
+
+<p>
+<em>Updating</em>:
+Code that uses packages in <code>go</code> will have to be updated by hand; the
+compiler will reject incorrect uses. Templates used in conjunction with any of the
+<code>go/doc</code> types may need manual fixes; the renamed fields will lead
+to run-time errors.
+</p>
+
+<h3 id="hash">The hash package</h3>
+
+<p>
+In Go 1, the definition of <a href="/pkg/hash/#Hash"><code>hash.Hash</code></a> includes
+a new method, <code>BlockSize</code>. This new method is used primarily in the
+cryptographic libraries.
+</p>
+
+<p>
+The <code>Sum</code> method of the
+<a href="/pkg/hash/#Hash"><code>hash.Hash</code></a> interface now takes a
+<code>[]byte</code> argument, to which the hash value will be appended.
+The previous behavior can be recreated by adding a <code>nil</code> argument to the call.
+</p>
+
+<p>
+<em>Updating</em>:
+Existing implementations of <code>hash.Hash</code> will need to add a
+<code>BlockSize</code> method. Hashes that process the input one byte at
+a time can implement <code>BlockSize</code> to return 1.
+Running <code>go</code> <code>fix</code> will update calls to the <code>Sum</code> methods of the various
+implementations of <code>hash.Hash</code>.
+</p>
+
+<p>
+<em>Updating</em>:
+Since the package's functionality is new, no updating is necessary.
+</p>
+
+<h3 id="http">The http package</h3>
+
+<p>
+In Go 1 the <a href="/pkg/net/http/"><code>http</code></a> package is refactored,
+putting some of the utilities into a
+<a href="/pkg/net/http/httputil/"><code>httputil</code></a> subdirectory.
+These pieces are only rarely needed by HTTP clients.
+The affected items are:
+</p>
+
+<ul>
+<li>ClientConn</li>
+<li>DumpRequest</li>
+<li>DumpRequestOut</li>
+<li>DumpResponse</li>
+<li>NewChunkedReader</li>
+<li>NewChunkedWriter</li>
+<li>NewClientConn</li>
+<li>NewProxyClientConn</li>
+<li>NewServerConn</li>
+<li>NewSingleHostReverseProxy</li>
+<li>ReverseProxy</li>
+<li>ServerConn</li>
+</ul>
+
+<p>
+The <code>Request.RawURL</code> field has been removed; it was a
+historical artifact.
+</p>
+
+<p>
+The <code>Handle</code> and <code>HandleFunc</code>
+functions, and the similarly-named methods of <code>ServeMux</code>,
+now panic if an attempt is made to register the same pattern twice.
+</p>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will update the few programs that are affected except for
+uses of <code>RawURL</code>, which must be fixed by hand.
+</p>
+
+<h3 id="image">The image package</h3>
+
+<p>
+The <a href="/pkg/image/"><code>image</code></a> package has had a number of
+minor changes, rearrangements and renamings.
+</p>
+
+<p>
+Most of the color handling code has been moved into its own package,
+<a href="/pkg/image/color/"><code>image/color</code></a>.
+For the elements that moved, a symmetry arises; for instance,
+each pixel of an
+<a href="/pkg/image/#RGBA"><code>image.RGBA</code></a>
+is a
+<a href="/pkg/image/color/#RGBA"><code>color.RGBA</code></a>.
+</p>
+
+<p>
+The old <code>image/ycbcr</code> package has been folded, with some
+renamings, into the
+<a href="/pkg/image/"><code>image</code></a>
+and
+<a href="/pkg/image/color/"><code>image/color</code></a>
+packages.
+</p>
+
+<p>
+The old <code>image.ColorImage</code> type is still in the <code>image</code>
+package but has been renamed
+<a href="/pkg/image/#Uniform"><code>image.Uniform</code></a>,
+while <code>image.Tiled</code> has been removed.
+</p>
+
+<p>
+This table lists the renamings.
+</p>
+
+<table class="codetable" frame="border" summary="image renames">
+<colgroup align="left" width="50%"></colgroup>
+<colgroup align="left" width="50%"></colgroup>
+<tr>
+<th align="left">Old</th>
+<th align="left">New</th>
+</tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>image.Color</td> <td>color.Color</td></tr>
+<tr><td>image.ColorModel</td> <td>color.Model</td></tr>
+<tr><td>image.ColorModelFunc</td> <td>color.ModelFunc</td></tr>
+<tr><td>image.PalettedColorModel</td> <td>color.Palette</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>image.RGBAColor</td> <td>color.RGBA</td></tr>
+<tr><td>image.RGBA64Color</td> <td>color.RGBA64</td></tr>
+<tr><td>image.NRGBAColor</td> <td>color.NRGBA</td></tr>
+<tr><td>image.NRGBA64Color</td> <td>color.NRGBA64</td></tr>
+<tr><td>image.AlphaColor</td> <td>color.Alpha</td></tr>
+<tr><td>image.Alpha16Color</td> <td>color.Alpha16</td></tr>
+<tr><td>image.GrayColor</td> <td>color.Gray</td></tr>
+<tr><td>image.Gray16Color</td> <td>color.Gray16</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>image.RGBAColorModel</td> <td>color.RGBAModel</td></tr>
+<tr><td>image.RGBA64ColorModel</td> <td>color.RGBA64Model</td></tr>
+<tr><td>image.NRGBAColorModel</td> <td>color.NRGBAModel</td></tr>
+<tr><td>image.NRGBA64ColorModel</td> <td>color.NRGBA64Model</td></tr>
+<tr><td>image.AlphaColorModel</td> <td>color.AlphaModel</td></tr>
+<tr><td>image.Alpha16ColorModel</td> <td>color.Alpha16Model</td></tr>
+<tr><td>image.GrayColorModel</td> <td>color.GrayModel</td></tr>
+<tr><td>image.Gray16ColorModel</td> <td>color.Gray16Model</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>ycbcr.RGBToYCbCr</td> <td>color.RGBToYCbCr</td></tr>
+<tr><td>ycbcr.YCbCrToRGB</td> <td>color.YCbCrToRGB</td></tr>
+<tr><td>ycbcr.YCbCrColorModel</td> <td>color.YCbCrModel</td></tr>
+<tr><td>ycbcr.YCbCrColor</td> <td>color.YCbCr</td></tr>
+<tr><td>ycbcr.YCbCr</td> <td>image.YCbCr</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>ycbcr.SubsampleRatio444</td> <td>image.YCbCrSubsampleRatio444</td></tr>
+<tr><td>ycbcr.SubsampleRatio422</td> <td>image.YCbCrSubsampleRatio422</td></tr>
+<tr><td>ycbcr.SubsampleRatio420</td> <td>image.YCbCrSubsampleRatio420</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>image.ColorImage</td> <td>image.Uniform</td></tr>
+</table>
+
+<p>
+The image package's <code>New</code> functions
+(<a href="/pkg/image/#NewRGBA"><code>NewRGBA</code></a>,
+<a href="/pkg/image/#NewRGBA64"><code>NewRGBA64</code></a>, etc.)
+take an <a href="/pkg/image/#Rectangle"><code>image.Rectangle</code></a> as an argument
+instead of four integers.
+</p>
+
+<p>
+Finally, there are new predefined <code>color.Color</code> variables
+<a href="/pkg/image/color/#Black"><code>color.Black</code></a>,
+<a href="/pkg/image/color/#White"><code>color.White</code></a>,
+<a href="/pkg/image/color/#Opaque"><code>color.Opaque</code></a>
+and
+<a href="/pkg/image/color/#Transparent"><code>color.Transparent</code></a>.
+</p>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will update almost all code affected by the change.
+</p>
+
+<h3 id="log_syslog">The log/syslog package</h3>
+
+<p>
+In Go 1, the <a href="/pkg/log/syslog/#NewLogger"><code>syslog.NewLogger</code></a>
+function returns an error as well as a <code>log.Logger</code>.
+</p>
+
+<p>
+<em>Updating</em>:
+What little code is affected will be caught by the compiler and must be updated by hand.
+</p>
+
+<h3 id="mime">The mime package</h3>
+
+<p>
+In Go 1, the <a href="/pkg/mime/#FormatMediaType"><code>FormatMediaType</code></a> function
+of the <code>mime</code> package has been simplified to make it
+consistent with
+<a href="/pkg/mime/#ParseMediaType"><code>ParseMediaType</code></a>.
+It now takes <code>"text/html"</code> rather than <code>"text"</code> and <code>"html"</code>.
+</p>
+
+<p>
+<em>Updating</em>:
+What little code is affected will be caught by the compiler and must be updated by hand.
+</p>
+
+<h3 id="net">The net package</h3>
+
+<p>
+In Go 1, the various <code>SetTimeout</code>,
+<code>SetReadTimeout</code>, and <code>SetWriteTimeout</code> methods
+have been replaced with
+<a href="/pkg/net/#IPConn.SetDeadline"><code>SetDeadline</code></a>,
+<a href="/pkg/net/#IPConn.SetReadDeadline"><code>SetReadDeadline</code></a>, and
+<a href="/pkg/net/#IPConn.SetWriteDeadline"><code>SetWriteDeadline</code></a>,
+respectively. Rather than taking a timeout value in nanoseconds that
+apply to any activity on the connection, the new methods set an
+absolute deadline (as a <code>time.Time</code> value) after which
+reads and writes will time out and no longer block.
+</p>
+
+<p>
+There are also new functions
+<a href="/pkg/net/#DialTimeout"><code>net.DialTimeout</code></a>
+to simplify timing out dialing a network address and
+<a href="/pkg/net/#ListenMulticastUDP"><code>net.ListenMulticastUDP</code></a>
+to allow multicast UDP to listen concurrently across multiple listeners.
+The <code>net.ListenMulticastUDP</code> function replaces the old
+<code>JoinGroup</code> and <code>LeaveGroup</code> methods.
+</p>
+
+<p>
+<em>Updating</em>:
+Code that uses the old methods will fail to compile and must be updated by hand.
+The semantic change makes it difficult for the fix tool to update automatically.
+</p>
+
+<h3 id="os">The os package</h3>
+
+<p>
+The <code>Time</code> function has been removed; callers should use
+the <a href="/pkg/time/#Time"><code>Time</code></a> type from the
+<code>time</code> package.
+</p>
+
+<p>
+The <code>Exec</code> function has been removed; callers should use
+<code>Exec</code> from the <code>syscall</code> package, where available.
+</p>
+
+<p>
+The <code>ShellExpand</code> function has been renamed to <a
+href="/pkg/os/#ExpandEnv"><code>ExpandEnv</code></a>.
+</p>
+
+<p>
+The <a href="/pkg/os/#NewFile"><code>NewFile</code></a> function
+now takes a <code>uintptr</code> fd, instead of an <code>int</code>.
+The <a href="/pkg/os/#File.Fd"><code>Fd</code></a> method on files now
+also returns a <code>uintptr</code>.
+</p>
+
+<p>
+There are no longer error constants such as <code>EINVAL</code>
+in the <code>os</code> package, since the set of values varied with
+the underlying operating system. There are new portable functions like
+<a href="/pkg/os/#IsPermission"><code>IsPermission</code></a>
+to test common error properties, plus a few new error values
+with more Go-like names, such as
+<a href="/pkg/os/#ErrPermission"><code>ErrPermission</code></a>
+and
+<a href="/pkg/os/#ErrNoEnv"><code>ErrNoEnv</code></a>.
+</p>
+
+<p>
+The <code>Getenverror</code> function has been removed. To distinguish
+between a non-existent environment variable and an empty string,
+use <a href="/pkg/os/#Environ"><code>os.Environ</code></a> or
+<a href="/pkg/syscall/#Getenv"><code>syscall.Getenv</code></a>.
+</p>
+
+
+<p>
+The <a href="/pkg/os/#Process.Wait"><code>Process.Wait</code></a> method has
+dropped its option argument and the associated constants are gone
+from the package.
+Also, the function <code>Wait</code> is gone; only the method of
+the <code>Process</code> type persists.
+</p>
+
+<p>
+The <code>Waitmsg</code> type returned by
+<a href="/pkg/os/#Process.Wait"><code>Process.Wait</code></a>
+has been replaced with a more portable
+<a href="/pkg/os/#ProcessState"><code>ProcessState</code></a>
+type with accessor methods to recover information about the
+process.
+Because of changes to <code>Wait</code>, the <code>ProcessState</code>
+value always describes an exited process.
+Portability concerns simplified the interface in other ways, but the values returned by the
+<a href="/pkg/os/#ProcessState.Sys"><code>ProcessState.Sys</code></a> and
+<a href="/pkg/os/#ProcessState.SysUsage"><code>ProcessState.SysUsage</code></a>
+methods can be type-asserted to underlying system-specific data structures such as
+<a href="/pkg/syscall/#WaitStatus"><code>syscall.WaitStatus</code></a> and
+<a href="/pkg/syscall/#Rusage"><code>syscall.Rusage</code></a> on Unix.
+</p>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will drop a zero argument to <code>Process.Wait</code>.
+All other changes will be caught by the compiler and must be updated by hand.
+</p>
+
+<h4 id="os_fileinfo">The os.FileInfo type</h4>
+
+<p>
+Go 1 redefines the <a href="/pkg/os/#FileInfo"><code>os.FileInfo</code></a> type,
+changing it from a struct to an interface:
+</p>
+
+<pre>
+ type FileInfo interface {
+ Name() string // base name of the file
+ Size() int64 // length in bytes
+ Mode() FileMode // file mode bits
+ ModTime() time.Time // modification time
+ IsDir() bool // abbreviation for Mode().IsDir()
+ Sys() interface{} // underlying data source (can return nil)
+ }
+</pre>
+
+<p>
+The file mode information has been moved into a subtype called
+<a href="/pkg/os/#FileMode"><code>os.FileMode</code></a>,
+a simple integer type with <code>IsDir</code>, <code>Perm</code>, and <code>String</code>
+methods.
+</p>
+
+<p>
+The system-specific details of file modes and properties such as (on Unix)
+i-number have been removed from <code>FileInfo</code> altogether.
+Instead, each operating system's <code>os</code> package provides an
+implementation of the <code>FileInfo</code> interface, which
+has a <code>Sys</code> method that returns the
+system-specific representation of file metadata.
+For instance, to discover the i-number of a file on a Unix system, unpack
+the <code>FileInfo</code> like this:
+</p>
+
+<pre>
+ fi, err := os.Stat("hello.go")
+ if err != nil {
+ log.Fatal(err)
+ }
+ // Check that it's a Unix file.
+ unixStat, ok := fi.Sys().(*syscall.Stat_t)
+ if !ok {
+ log.Fatal("hello.go: not a Unix file")
+ }
+ fmt.Printf("file i-number: %d\n", unixStat.Ino)
+</pre>
+
+<p>
+Assuming (which is unwise) that <code>"hello.go"</code> is a Unix file,
+the i-number expression could be contracted to
+</p>
+
+<pre>
+ fi.Sys().(*syscall.Stat_t).Ino
+</pre>
+
+<p>
+The vast majority of uses of <code>FileInfo</code> need only the methods
+of the standard interface.
+</p>
+
+<p>
+The <code>os</code> package no longer contains wrappers for the POSIX errors
+such as <code>ENOENT</code>.
+For the few programs that need to verify particular error conditions, there are
+now the boolean functions
+<a href="/pkg/os/#IsExist"><code>IsExist</code></a>,
+<a href="/pkg/os/#IsNotExist"><code>IsNotExist</code></a>
+and
+<a href="/pkg/os/#IsPermission"><code>IsPermission</code></a>.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/os\.Open/` `/}/`}}
+--> f, err := os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
+ if os.IsExist(err) {
+ log.Printf(&#34;%s already exists&#34;, name)
+ }</pre>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will update code that uses the old equivalent of the current <code>os.FileInfo</code>
+and <code>os.FileMode</code> API.
+Code that needs system-specific file details will need to be updated by hand.
+Code that uses the old POSIX error values from the <code>os</code> package
+will fail to compile and will also need to be updated by hand.
+</p>
+
+<h3 id="os_signal">The os/signal package</h3>
+
+<p>
+The <code>os/signal</code> package in Go 1 replaces the
+<code>Incoming</code> function, which returned a channel
+that received all incoming signals,
+with the selective <code>Notify</code> function, which asks
+for delivery of specific signals on an existing channel.
+</p>
+
+<p>
+<em>Updating</em>:
+Code must be updated by hand.
+A literal translation of
+</p>
+<pre>
+c := signal.Incoming()
+</pre>
+<p>
+is
+</p>
+<pre>
+c := make(chan os.Signal)
+signal.Notify(c) // ask for all signals
+</pre>
+<p>
+but most code should list the specific signals it wants to handle instead:
+</p>
+<pre>
+c := make(chan os.Signal)
+signal.Notify(c, syscall.SIGHUP, syscall.SIGQUIT)
+</pre>
+
+<h3 id="path_filepath">The path/filepath package</h3>
+
+<p>
+In Go 1, the <a href="/pkg/path/filepath/#Walk"><code>Walk</code></a> function of the
+<code>path/filepath</code> package
+has been changed to take a function value of type
+<a href="/pkg/path/filepath/#WalkFunc"><code>WalkFunc</code></a>
+instead of a <code>Visitor</code> interface value.
+<code>WalkFunc</code> unifies the handling of both files and directories.
+</p>
+
+<pre>
+ type WalkFunc func(path string, info os.FileInfo, err error) error
+</pre>
+
+<p>
+The <code>WalkFunc</code> function will be called even for files or directories that could not be opened;
+in such cases the error argument will describe the failure.
+If a directory's contents are to be skipped,
+the function should return the value <a href="/pkg/path/filepath/#variables"><code>filepath.SkipDir</code></a>
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/STARTWALK/` `/ENDWALK/`}}
+--> markFn := func(path string, info os.FileInfo, err error) error {
+ if path == &#34;pictures&#34; { <span class="comment">// Will skip walking of directory pictures and its contents.</span>
+ return filepath.SkipDir
+ }
+ if err != nil {
+ return err
+ }
+ log.Println(path)
+ return nil
+ }
+ err := filepath.Walk(&#34;.&#34;, markFn)
+ if err != nil {
+ log.Fatal(err)
+ }</pre>
+
+<p>
+<em>Updating</em>:
+The change simplifies most code but has subtle consequences, so affected programs
+will need to be updated by hand.
+The compiler will catch code using the old interface.
+</p>
+
+<h3 id="regexp">The regexp package</h3>
+
+<p>
+The <a href="/pkg/regexp/"><code>regexp</code></a> package has been rewritten.
+It has the same interface but the specification of the regular expressions
+it supports has changed from the old "egrep" form to that of
+<a href="http://code.google.com/p/re2/">RE2</a>.
+</p>
+
+<p>
+<em>Updating</em>:
+Code that uses the package should have its regular expressions checked by hand.
+</p>
+
+<h3 id="runtime">The runtime package</h3>
+
+<p>
+In Go 1, much of the API exported by package
+<code>runtime</code> has been removed in favor of
+functionality provided by other packages.
+Code using the <code>runtime.Type</code> interface
+or its specific concrete type implementations should
+now use package <a href="/pkg/reflect/"><code>reflect</code></a>.
+Code using <code>runtime.Semacquire</code> or <code>runtime.Semrelease</code>
+should use channels or the abstractions in package <a href="/pkg/sync/"><code>sync</code></a>.
+The <code>runtime.Alloc</code>, <code>runtime.Free</code>,
+and <code>runtime.Lookup</code> functions, an unsafe API created for
+debugging the memory allocator, have no replacement.
+</p>
+
+<p>
+Before, <code>runtime.MemStats</code> was a global variable holding
+statistics about memory allocation, and calls to <code>runtime.UpdateMemStats</code>
+ensured that it was up to date.
+In Go 1, <code>runtime.MemStats</code> is a struct type, and code should use
+<a href="/pkg/runtime/#ReadMemStats"><code>runtime.ReadMemStats</code></a>
+to obtain the current statistics.
+</p>
+
+<p>
+The package adds a new function,
+<a href="/pkg/runtime/#NumCPU"><code>runtime.NumCPU</code></a>, that returns the number of CPUs available
+for parallel execution, as reported by the operating system kernel.
+Its value can inform the setting of <code>GOMAXPROCS</code>.
+The <code>runtime.Cgocalls</code> and <code>runtime.Goroutines</code> functions
+have been renamed to <code>runtime.NumCgoCall</code> and <code>runtime.NumGoroutine</code>.
+</p>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will update code for the function renamings.
+Other code will need to be updated by hand.
+</p>
+
+<h3 id="strconv">The strconv package</h3>
+
+<p>
+In Go 1, the
+<a href="/pkg/strconv/"><code>strconv</code></a>
+package has been significantly reworked to make it more Go-like and less C-like,
+although <code>Atoi</code> lives on (it's similar to
+<code>int(ParseInt(x, 10, 0))</code>, as does
+<code>Itoa(x)</code> (<code>FormatInt(int64(x), 10)</code>).
+There are also new variants of some of the functions that append to byte slices rather than
+return strings, to allow control over allocation.
+</p>
+
+<p>
+This table summarizes the renamings; see the
+<a href="/pkg/strconv/">package documentation</a>
+for full details.
+</p>
+
+<table class="codetable" frame="border" summary="strconv renames">
+<colgroup align="left" width="50%"></colgroup>
+<colgroup align="left" width="50%"></colgroup>
+<tr>
+<th align="left">Old call</th>
+<th align="left">New call</th>
+</tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>Atob(x)</td> <td>ParseBool(x)</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>Atof32(x)</td> <td>ParseFloat(x, 32)§</td></tr>
+<tr><td>Atof64(x)</td> <td>ParseFloat(x, 64)</td></tr>
+<tr><td>AtofN(x, n)</td> <td>ParseFloat(x, n)</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>Atoi(x)</td> <td>Atoi(x)</td></tr>
+<tr><td>Atoi(x)</td> <td>ParseInt(x, 10, 0)§</td></tr>
+<tr><td>Atoi64(x)</td> <td>ParseInt(x, 10, 64)</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>Atoui(x)</td> <td>ParseUint(x, 10, 0)§</td></tr>
+<tr><td>Atoui64(x)</td> <td>ParseUint(x, 10, 64)</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>Btoi64(x, b)</td> <td>ParseInt(x, b, 64)</td></tr>
+<tr><td>Btoui64(x, b)</td> <td>ParseUint(x, b, 64)</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>Btoa(x)</td> <td>FormatBool(x)</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>Ftoa32(x, f, p)</td> <td>FormatFloat(float64(x), f, p, 32)</td></tr>
+<tr><td>Ftoa64(x, f, p)</td> <td>FormatFloat(x, f, p, 64)</td></tr>
+<tr><td>FtoaN(x, f, p, n)</td> <td>FormatFloat(x, f, p, n)</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>Itoa(x)</td> <td>Itoa(x)</td></tr>
+<tr><td>Itoa(x)</td> <td>FormatInt(int64(x), 10)</td></tr>
+<tr><td>Itoa64(x)</td> <td>FormatInt(x, 10)</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>Itob(x, b)</td> <td>FormatInt(int64(x), b)</td></tr>
+<tr><td>Itob64(x, b)</td> <td>FormatInt(x, b)</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>Uitoa(x)</td> <td>FormatUint(uint64(x), 10)</td></tr>
+<tr><td>Uitoa64(x)</td> <td>FormatUint(x, 10)</td></tr>
+<tr>
+<td colspan="2"><hr></td>
+</tr>
+<tr><td>Uitob(x, b)</td> <td>FormatUint(uint64(x), b)</td></tr>
+<tr><td>Uitob64(x, b)</td> <td>FormatUint(x, b)</td></tr>
+</table>
+
+<p>
+<em>Updating</em>:
+Running <code>go</code> <code>fix</code> will update almost all code affected by the change.
+<br>
+§ <code>Atoi</code> persists but <code>Atoui</code> and <code>Atof32</code> do not, so
+they may require
+a cast that must be added by hand; the <code>go</code> <code>fix</code> tool will warn about it.
+</p>
+
+
+<h3 id="templates">The template packages</h3>
+
+<p>
+The <code>template</code> and <code>exp/template/html</code> packages have moved to
+<a href="/pkg/text/template/"><code>text/template</code></a> and
+<a href="/pkg/html/template/"><code>html/template</code></a>.
+More significant, the interface to these packages has been simplified.
+The template language is the same, but the concept of "template set" is gone
+and the functions and methods of the packages have changed accordingly,
+often by elimination.
+</p>
+
+<p>
+Instead of sets, a <code>Template</code> object
+may contain multiple named template definitions,
+in effect constructing
+name spaces for template invocation.
+A template can invoke any other template associated with it, but only those
+templates associated with it.
+The simplest way to associate templates is to parse them together, something
+made easier with the new structure of the packages.
+</p>
+
+<p>
+<em>Updating</em>:
+The imports will be updated by fix tool.
+Single-template uses will be otherwise be largely unaffected.
+Code that uses multiple templates in concert will need to be updated by hand.
+The <a href="/pkg/text/template/#examples">examples</a> in
+the documentation for <code>text/template</code> can provide guidance.
+</p>
+
+<h3 id="testing">The testing package</h3>
+
+<p>
+The testing package has a type, <code>B</code>, passed as an argument to benchmark functions.
+In Go 1, <code>B</code> has new methods, analogous to those of <code>T</code>, enabling
+logging and failure reporting.
+</p>
+
+<pre><!--{{code "/doc/progs/go1.go" `/func.*Benchmark/` `/^}/`}}
+-->func BenchmarkSprintf(b *testing.B) {
+ <span class="comment">// Verify correctness before running benchmark.</span>
+ b.StopTimer()
+ got := fmt.Sprintf(&#34;%x&#34;, 23)
+ const expect = &#34;17&#34;
+ if expect != got {
+ b.Fatalf(&#34;expected %q; got %q&#34;, expect, got)
+ }
+ b.StartTimer()
+ for i := 0; i &lt; b.N; i++ {
+ fmt.Sprintf(&#34;%x&#34;, 23)
+ }
+}</pre>
+
+<p>
+<em>Updating</em>:
+Existing code is unaffected, although benchmarks that use <code>println</code>
+or <code>panic</code> should be updated to use the new methods.
+</p>
+
+<h3 id="testing_script">The testing/script package</h3>
+
+<p>
+The testing/script package has been deleted. It was a dreg.
+</p>
+
+<p>
+<em>Updating</em>:
+No code is likely to be affected.
+</p>
+
+<h3 id="unsafe">The unsafe package</h3>
+
+<p>
+In Go 1, the functions
+<code>unsafe.Typeof</code>, <code>unsafe.Reflect</code>,
+<code>unsafe.Unreflect</code>, <code>unsafe.New</code>, and
+<code>unsafe.NewArray</code> have been removed;
+they duplicated safer functionality provided by
+package <a href="/pkg/reflect/"><code>reflect</code></a>.
+</p>
+
+<p>
+<em>Updating</em>:
+Code using these functions must be rewritten to use
+package <a href="/pkg/reflect/"><code>reflect</code></a>.
+The changes to <a href="http://code.google.com/p/go/source/detail?r=2646dc956207">encoding/gob</a> and the <a href="http://code.google.com/p/goprotobuf/source/detail?r=5340ad310031">protocol buffer library</a>
+may be helpful as examples.
+</p>
+
+<h3 id="url">The url package</h3>
+
+<p>
+In Go 1 several fields from the <a href="/pkg/net/url/#URL"><code>url.URL</code></a> type
+were removed or replaced.
+</p>
+
+<p>
+The <a href="/pkg/net/url/#URL.String"><code>String</code></a> method now
+predictably rebuilds an encoded URL string using all of <code>URL</code>'s
+fields as necessary. The resulting string will also no longer have
+passwords escaped.
+</p>
+
+<p>
+The <code>Raw</code> field has been removed. In most cases the <code>String</code>
+method may be used in its place.
+</p>
+
+<p>
+The old <code>RawUserinfo</code> field is replaced by the <code>User</code>
+field, of type <a href="/pkg/net/url/#Userinfo"><code>*net.Userinfo</code></a>.
+Values of this type may be created using the new <a href="/pkg/net/url/#User"><code>net.User</code></a>
+and <a href="/pkg/net/url/#UserPassword"><code>net.UserPassword</code></a>
+functions. The <code>EscapeUserinfo</code> and <code>UnescapeUserinfo</code>
+functions are also gone.
+</p>
+
+<p>
+The <code>RawAuthority</code> field has been removed. The same information is
+available in the <code>Host</code> and <code>User</code> fields.
+</p>
+
+<p>
+The <code>RawPath</code> field and the <code>EncodedPath</code> method have
+been removed. The path information in rooted URLs (with a slash following the
+schema) is now available only in decoded form in the <code>Path</code> field.
+Occasionally, the encoded data may be required to obtain information that
+was lost in the decoding process. These cases must be handled by accessing
+the data the URL was built from.
+</p>
+
+<p>
+URLs with non-rooted paths, such as <code>"mailto:dev@golang.org?subject=Hi"</code>,
+are also handled differently. The <code>OpaquePath</code> boolean field has been
+removed and a new <code>Opaque</code> string field introduced to hold the encoded
+path for such URLs. In Go 1, the cited URL parses as:
+</p>
+
+<pre>
+ URL{
+ Scheme: "mailto",
+ Opaque: "dev@golang.org",
+ RawQuery: "subject=Hi",
+ }
+</pre>
+
+<p>
+A new <a href="/pkg/net/url/#URL.RequestURI"><code>RequestURI</code></a> method was
+added to <code>URL</code>.
+</p>
+
+<p>
+The <code>ParseWithReference</code> function has been renamed to <code>ParseWithFragment</code>.
+</p>
+
+<p>
+<em>Updating</em>:
+Code that uses the old fields will fail to compile and must be updated by hand.
+The semantic changes make it difficult for the fix tool to update automatically.
+</p>
+
+<h2 id="cmd_go">The go command</h2>
+
+<p>
+Go 1 introduces the <a href="/cmd/go/">go command</a>, a tool for fetching,
+building, and installing Go packages and commands. The <code>go</code> command
+does away with makefiles, instead using Go source code to find dependencies and
+determine build conditions. Most existing Go programs will no longer require
+makefiles to be built.
+</p>
+
+<p>
+See <a href="/doc/code.html">How to Write Go Code</a> for a primer on the
+<code>go</code> command and the <a href="/cmd/go/">go command documentation</a>
+for the full details.
+</p>
+
+<p>
+<em>Updating</em>:
+Projects that depend on the Go project's old makefile-based build
+infrastructure (<code>Make.pkg</code>, <code>Make.cmd</code>, and so on) should
+switch to using the <code>go</code> command for building Go code and, if
+necessary, rewrite their makefiles to perform any auxiliary build tasks.
+</p>
+
+<h2 id="cmd_cgo">The cgo command</h2>
+
+<p>
+In Go 1, the <a href="/cmd/cgo">cgo command</a>
+uses a different <code>_cgo_export.h</code>
+file, which is generated for packages containing <code>//export</code> lines.
+The <code>_cgo_export.h</code> file now begins with the C preamble comment,
+so that exported function definitions can use types defined there.
+This has the effect of compiling the preamble multiple times, so a
+package using <code>//export</code> must not put function definitions
+or variable initializations in the C preamble.
+</p>
+
+<h2 id="releases">Packaged releases</h2>
+
+<p>
+One of the most significant changes associated with Go 1 is the availability
+of prepackaged, downloadable distributions.
+They are available for many combinations of architecture and operating system
+(including Windows) and the list will grow.
+Installation details are described on the
+<a href="/doc/install">Getting Started</a> page, while
+the distributions themselves are listed on the
+<a href="http://code.google.com/p/go/downloads/list">downloads page</a>.
+
+
+</div>
+
+<div id="footer">
+Build version go1.0.1.<br>
+A link <a href="http://code.google.com/policies.html#restrictions">noted</a>,
+and then, coming up on the very next line, we will
+find yet another link, link 3.0 if you will,
+after a few more words <a href="/LINK">link text</a>.<br>
+<a href="/doc/tos.html">Terms of Service</a> |
+<a href="http://www.google.com/intl/en/privacy/privacy-policy.html">Privacy Policy</a>
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