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<!-- Release History -->
<p>This page summarizes the changes between official stable releases of Go.
Between releases we issue less stable
<a href="">weekly snapshots</a>.
The <a href="weekly.html">weekly snapshot history</a> contains more detail,
and the <a href="">Mercurial change log</a>
has full details.</p>
<p>To update to a specific release, use:</p>
hg pull
hg update release.r<i>NN</i>
<h2 id="r57">r57 (released 2011/05/03)</h2>
The r57 release corresponds to
<code><a href="weekly.html#2011-04-27">weekly.2011-04-27</a></code>
with additional bug fixes.
This section highlights the most significant changes in this release.
For a more detailed summary, see the
<a href="weekly.html#2011-04-27">weekly release notes</a>.
For complete information, see the
<a href="">Mercurial change list</a>.
<p>The new <a href="/cmd/gofix">gofix</a> tool finds Go programs that use old APIs and rewrites them to use
newer ones. After you update to a new Go release, gofix helps make the
necessary changes to your programs. Gofix will handle the http, os, and syscall
package changes described below, and we will update the program to keep up with
future changes to the libraries.
Gofix can’t
handle all situations perfectly, so read and test the changes it makes before
committing them.
See <a href="">the gofix blog post</a> for more
<h3 id="r57.lang">Language</h3>
<a href="/doc/go_spec.html#Receive_operator">Multiple assignment syntax</a> replaces the <code>closed</code> function.
The syntax for channel
receives allows an optional second assigned value, a boolean value
indicating whether the channel is closed. This code:
v := &lt;-ch
if closed(ch) {
// channel is closed
<p>should now be written as:</p>
v, ok := &lt;-ch
if !ok {
// channel is closed
<p><a href="/doc/go_spec.html#Label_scopes">Unused labels are now illegal</a>, just as unused local variables are.</p>
<h3 id="r57.pkg">Packages</h3>
<a href="/pkg/gob/">Package gob</a> will now encode and decode values of types that implement the
<a href="/pkg/gob/#GobEncoder">GobEncoder</a> and
<a href="/pkg/gob/#GobDecoder">GobDecoder</a> interfaces. This allows types with unexported
fields to transmit self-consistent descriptions; examples include
<a href="/pkg/big/#Int.GobDecode">big.Int</a> and <a href="/pkg/big/#Rat.GobDecode">big.Rat</a>.
<a href="/pkg/http/">Package http</a> has been redesigned.
For clients, there are new
<a href="/pkg/http/#Client">Client</a> and <a href="/pkg/http/#Transport">Transport</a>
abstractions that give more control over HTTP details such as headers sent
and redirections followed. These abstractions make it easy to implement
custom clients that add functionality such as <a href="">OAuth2</a>.
For servers, <a href="/pkg/http/#ResponseWriter">ResponseWriter</a>
has dropped its non-essential methods.
The Hijack and Flush methods are no longer required;
code can test for them by checking whether a specific value implements
<a href="/pkg/http/#Hijacker">Hijacker</a> or <a href="/pkg/http/#Flusher">Flusher</a>.
The RemoteAddr and UsingTLS methods are replaced by <a href="/pkg/http/#Request">Request</a>'s
RemoteAddr and TLS fields.
The SetHeader method is replaced by a Header method;
its result, of type <a href="/pkg/http/#Header">Header</a>,
implements Set and other methods.
<a href="/pkg/net/">Package net</a>
drops the <code>laddr</code> argument from <a href="/pkg/net/#Conn.Dial">Dial</a>
and drops the <code>cname</code> return value
from <a href="/pkg/net/#LookupHost">LookupHost</a>.
The implementation now uses <a href="/cmd/cgo/">cgo</a> to implement
network name lookups using the C library getaddrinfo(3)
function when possible. This ensures that Go and C programs
resolve names the same way and also avoids the OS X
application-level firewall.
<a href="/pkg/os/">Package os</a>
introduces simplified <a href="/pkg/os/#File.Open">Open</a>
and <a href="/pkg/os/#File.Create">Create</a> functions.
The original Open is now available as <a href="/pkg/os/#File.OpenFile">OpenFile</a>.
The final three arguments to <a href="/pkg/os/#Process.StartProcess">StartProcess</a>
have been replaced by a pointer to a <a href="/pkg/os/#ProcAttr">ProcAttr</a>.
<a href="/pkg/reflect/">Package reflect</a> has been redesigned.
<a href="/pkg/reflect/#Type">Type</a> is now an interface that implements
all the possible type methods.
Instead of a type switch on a Type <code>t</code>, switch on <code>t.Kind()</code>.
<a href="/pkg/reflect/#Value">Value</a> is now a struct value that
implements all the possible value methods.
Instead of a type switch on a Value <code>v</code>, switch on <code>v.Kind()</code>.
Typeof and NewValue are now called <a href="/pkg/reflect/#Type.TypeOf">TypeOf</a> and <a href="/pkg/reflect/#Value.ValueOf">ValueOf</a>
To create a writable Value, use <code>New(t).Elem()</code> instead of <code>Zero(t)</code>.
See <a href="">the change description</a>
for the full details.
The new API allows a more efficient implementation of Value
that avoids many of the allocations required by the previous API.
Remember that gofix will handle the bulk of the rewrites
necessary for these changes to package APIs.
<h3 id="r57.tool">Tools</h3>
<p><a href="/cmd/gofix/">Gofix</a>, a new command, is described above.</p>
<a href="/cmd/gotest/">Gotest</a> is now a Go program instead of a shell script.
The new <code>-test.short</code> flag in combination with package testing's Short function
allows you to write tests that can be run in normal or &ldquo;short&rdquo; mode;
all.bash runs tests in short mode to reduce installation time.
The Makefiles know about the flag: use <code>make testshort</code>.
The run-time support now implements CPU and memory profiling.
Gotest's new
<a href="/cmd/gotest/"><code>-test.cpuprofile</code> and
<code>-test.memprofile</code> flags</a> make it easy to
profile tests.
To add profiling to your web server, see the <a href="/pkg/http/pprof/">http/pprof</a>
For other uses, see the <a href="/pkg/runtime/pprof/">runtime/pprof</a> documentation.
<h3 id="r57.minor">Minor revisions</h3>
<p>r57.1 fixes a <a href="">nil pointer dereference in http.FormFile</a>.</p>
<h2 id="r56">r56 (released 2011/03/16)</h2>
The r56 release was the first stable release and corresponds to
<code><a href="weekly.html#2011-03-07">weekly.2011-03-07.1</a></code>.
The numbering starts at 56 because before this release,
what we now consider weekly snapshots were called releases.