This page summarizes the changes between official stable releases of Go. Between releases we issue less stable weekly snapshots. The weekly snapshot history contains more detail, and the Mercurial change log has full details.

To update to a specific release, use:

    hg pull
    hg update release.rNN

## r57 (released 2011/05/03)

The r57 release corresponds to `weekly.2011-04-27` with additional bug fixes. This section highlights the most significant changes in this release. For a more detailed summary, see the weekly release notes. For complete information, see the Mercurial change list.

The new gofix 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 the gofix blog post for more information.

### Language

Multiple assignment syntax replaces the `closed` function. The syntax for channel receives allows an optional second assigned value, a boolean value indicating whether the channel is closed. This code:

    	v := <-ch
    	if closed(ch) {
    		// channel is closed
    	}

should now be written as:

    	v, ok := <-ch
    	if !ok {
    		// channel is closed
    	}

Unused labels are now illegal, just as unused local variables are.

### Packages

Package gob will now encode and decode values of types that implement the GobEncoder and GobDecoder interfaces. This allows types with unexported fields to transmit self-consistent descriptions; examples include big.Int and big.Rat.

Package http has been redesigned. For clients, there are new Client and Transport 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 OAuth2. For servers, ResponseWriter 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 Hijacker or Flusher. The RemoteAddr and UsingTLS methods are replaced by Request's RemoteAddr and TLS fields. The SetHeader method is replaced by a Header method; its result, of type Header, implements Set and other methods.

Package net drops the `laddr` argument from Dial and drops the `cname` return value from LookupHost. The implementation now uses cgo 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.

Package os introduces simplified Open and Create functions. The original Open is now available as OpenFile. The final three arguments to StartProcess have been replaced by a pointer to a ProcAttr.

Package reflect has been redesigned. Type is now an interface that implements all the possible type methods. Instead of a type switch on a Type `t`, switch on `t.Kind()`. Value is now a struct value that implements all the possible value methods. Instead of a type switch on a Value `v`, switch on `v.Kind()`. Typeof and NewValue are now called TypeOf and ValueOf To create a writable Value, use `New(t).Elem()` instead of `Zero(t)`. See the change description 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.

### Tools

Gofix, a new command, is described above.

Gotest is now a Go program instead of a shell script. The new `-test.short` flag in combination with package testing's Short function allows you to write tests that can be run in normal or “short” mode; all.bash runs tests in short mode to reduce installation time. The Makefiles know about the flag: use `make testshort`.

The run-time support now implements CPU and memory profiling. Gotest's new `-test.cpuprofile` and `-test.memprofile` flags make it easy to profile tests. To add profiling to your web server, see the http/pprof documentation. For other uses, see the runtime/pprof documentation.

### Minor revisions

r57.1 fixes a nil pointer dereference in http.FormFile.

## r56 (released 2011/03/16)

The r56 release was the first stable release and corresponds to `weekly.2011-03-07.1`. The numbering starts at 56 because before this release, what we now consider weekly snapshots were called releases.