mirror of
https://github.com/golang/go
synced 2024-11-12 01:10:21 -07:00
2e338fa69f
R=rsc CC=golang-dev https://golang.org/cl/5478047
596 lines
17 KiB
HTML
596 lines
17 KiB
HTML
<!-- Go 1 Release Notes -->
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<!--
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DO NOT EDIT: created by
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tmpltohtml go1.tmpl
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-->
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<h2 id="introduction">Introduction to Go 1</h2>
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<p>
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For a full explanation of the motivation and design of Go 1, see XXX.
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Here follows a summary.
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</p>
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<p>
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Go 1 is intended to be a stable language and core library set that
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will form a reliable foundation for people and organizations that
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want to make a long-term commitment to developing in the Go programming
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language. Go will continue to develop, but in a way that guarantees
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code written to the Go 1 specification will continue to work. For
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instance, Go 1 will be a supported platform on Google App Engine
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for the next few years. Incompatible changes to the environment,
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should they arise, will be done in a distinct version.
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</p>
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<p>
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This document describes the changes in the language and libraries
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in Go 1, relative to the previous release, r60 (at the time of
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writing, tagged as r60.3). It also explains how to update code at
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r60 to compile and run under Go 1. Finally, it outlines the new
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<code>go</code> command for building Go programs and the new binary
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release process being introduced. Most of these topics have more
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thorough presentations elsewhere; such documents are linked below.
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</p>
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<h2 id="language">Changes to the language</h2>
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<h3 id="append">Append</h3>
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<p>
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The <code>append</code> built-in function is variadic, so one can
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append to a byte slice using the <code>...</code> syntax in the
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call.
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</p>
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<pre><!--{{code "progs/go1.go" `/greeting := ..byte/` `/append.*hello/`}}
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--> greeting := []byte{}
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greeting = append(greeting, []byte("hello ")...)
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</pre>
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<p>
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By analogy with the similar property of <code>copy</code>, Go 1
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permits a string to be appended (byte-wise) directly to a byte
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slice; the conversion is no longer necessary:
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</p>
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<pre><!--{{code "progs/go1.go" `/append.*world/`}}
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--> greeting = append(greeting, "world"...)
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</pre>
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<p>
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<em>Updating</em>:
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This is a new feature, so existing code needs no changes.
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</p>
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<h3 id="close">Close</h3>
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<p>
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The <code>close</code> built-in function lets a sender tell a receiver
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that no more data will be transmitted on the channel. In Go 1 the
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type system enforces the directionality when possible: it is illegal
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to call <code>close</code> on a receive-only channel:
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</p>
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<pre>
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var c chan int
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var csend chan<- int = c
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var crecv <-chan int = c
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close(c) // legal
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close(csend) // legal
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close(crecv) // illegal
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</pre>
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<p>
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<em>Updating</em>:
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Existing code that attempts to close a receive-only channel was
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erroneous even before Go 1 and should be fixed. The compiler will
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now reject such code.
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</p>
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<h3 id="literals">Composite literals</h3>
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<p>
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In Go 1, a composite literal of array, slice, or map type can elide the
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type specification for the elements' initializers if they are of pointer type.
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All four of the initializations in this example are legal; the last one was illegal before Go 1.
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</p>
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<pre><!--{{code "progs/go1.go" `/type Date struct/` `/STOP/`}}
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--> type Date struct {
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month string
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day int
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}
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// Struct values, fully qualified; always legal.
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holiday1 := []Date{
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Date{"Feb", 14},
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Date{"Nov", 11},
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Date{"Dec", 25},
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}
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// Struct values, type name elided; always legal.
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holiday2 := []Date{
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{"Feb", 14},
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{"Nov", 11},
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{"Dec", 25},
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}
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// Pointers, fully qualified, always legal.
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holiday3 := []*Date{
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&Date{"Feb", 14},
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&Date{"Nov", 11},
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&Date{"Dec", 25},
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}
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// Pointers, type name elided; legal in Go 1.
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holiday4 := []*Date{
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{"Feb", 14},
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{"Nov", 11},
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{"Dec", 25},
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}
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</pre>
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<p>
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<em>Updating</em>:
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This change has no effect on existing code, but the command
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<code>gofmt</code> <code>-s</code> applied to existing source
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will, among other things, elide explicit element types wherever permitted.
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</p>
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<h3 id="init">Goroutines during init</h3>
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<p>
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Go 1 allows goroutines to be created and run during initialization.
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(They used to be created but were not run until after initialization
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completed.) Code that uses goroutines can now be called from
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<code>init</code> routines and global initialization expressions
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without introducing a deadlock.
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</p>
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<pre><!--{{code "progs/go1.go" `/PackageGlobal/` `/^}/`}}
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-->var PackageGlobal int
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func init() {
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c := make(chan int)
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go initializationFunction(c)
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PackageGlobal = <-c
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}
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</pre>
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<p>
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<em>Updating</em>:
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This is a new feature, so existing code needs no changes,
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although it's possible that code that depends on goroutines not starting before <code>main</code> will break.
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There was no such code in the standard repository.
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</p>
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<h3 id="rune">The rune type</h3>
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<p>
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Go 1 introduces a new basic type, <code>rune</code>, to be used to represent
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individual Unicode code points.
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It is an alias for <code>int32</code>, analogous to <code>byte</code>
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as an alias for <code>uint8</code>.
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</p>
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<p>
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Character literals such as <code>'a'</code>, <code>'語'</code>, and <code>'\u0345'</code>
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now have default type <code>rune</code>,
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analogous to <code>1.0</code> having default type <code>float64</code>.
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A variable initialized to a character constant will therefore
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have type <code>rune</code> unless otherwise specified.
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</p>
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<p>
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Libraries have been updated to use <code>rune</code> rather than <code>int</code>
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when appropriate. For instance, the functions <code>unicode.ToLower</code> and
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relatives now take and return a <code>rune</code>.
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</p>
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<pre><!--{{code "progs/go1.go" `/STARTRUNE/` `/ENDRUNE/`}}
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--> delta := 'δ' // delta has type rune.
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var DELTA rune
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DELTA = unicode.ToUpper(delta)
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epsilon := unicode.ToLower(DELTA + 1)
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if epsilon != 'δ'+1 {
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log.Fatal("inconsistent casing for Greek")
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}
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</pre>
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<p>
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<em>Updating</em>:
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Most source code will be unaffected by this because the type inference from
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<code>:=</code> initializers introduces the new type silently, and it propagates
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from there.
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Some code may get type errors that a trivial conversion will resolve.
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</p>
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<h3 id="error">The error type</h3>
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<p>
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Go 1 introduces a new built-in type, <code>error</code>, which has the following definition:
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</p>
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<pre>
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type error interface {
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Error() string
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}
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</pre>
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<p>
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Since the consequences of this type are all in the package library,
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it is discussed <a href="errors">below</a>.
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</p>
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<h3 id="delete">Deleting from maps</h3>
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<p>
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The original syntax for deleting an element in a map was:
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</p>
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<pre>
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m[k] = ignored, false
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</pre>
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<p>
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In Go 1, that syntax has gone; instead there is a new built-in
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function, <code>delete</code>. The call
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</p>
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<pre><!--{{code "progs/go1.go" `/delete\(m, k\)/`}}
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--> delete(m, k)
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</pre>
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<p>
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will delete the map entry retrieved by the expression <code>m[k]</code>.
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There is no return value. Deleting a non-existent entry is a no-op.
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</p>
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<p>
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<em>Updating</em>:
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Gofix will convert expressions of the form <code>m[k] = ignored,
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false</code> into <code>delete(m, k)</code> when it is clear that
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the ignored value can be safely discarded from the program and
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<code>false</code> refers to the predefined boolean constant. Gofix
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will flag other uses of the syntax for inspection by the programmer.
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</p>
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<h3 id="iteration">Iterating in maps</h3>
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<p>
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In Go 1, the order in which elements are visited when iterating
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over a map using a <code>for</code> <code>range</code> statement
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is defined to be unpredictable, even if the same loop is run multiple
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times with the same map.
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Code should not assume that the elements are visited in any particular order.
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</p>
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<pre><!--{{code "progs/go1.go" `/Sunday/` `/^ }/`}}
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--> m := map[string]int{"Sunday": 0, "Monday": 1}
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for name, value := range m {
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// This loop should not assume Sunday will be visited first.
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f(name, value)
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}
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</pre>
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<p>
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<em>Updating</em>:
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This is one change where tools cannot help. Most existing code
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will be unaffected, but some programs may break or misbehave; we
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recommend manual checking of all range statements over maps to
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verify they do not depend on iteration order. There were a few such
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examples in the standard repository; they have been fixed.
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Note that it was already incorrect to depend on the iteration order, which
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was unspecified. This change codifies the unpredictability.
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</p>
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<h3 id="multiple_assignment">Multiple assignment</h3>
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<p>
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Go 1 fully specifies the evaluation order in multiple assignment
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statements. In particular, if the left-hand side of the assignment
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statement contains expressions that require evaluation, such as
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function calls or array indexing operations, these will all be done
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using the usual left-to-right rule before any variables are assigned
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their value. Once everything is evaluated, the actual assignments
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proceed in left-to-right order.
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</p>
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<p>
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These examples illustrate the behavior.
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</p>
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<pre><!--{{code "progs/go1.go" `/sa :=/` `/then sc.0. = 2/`}}
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--> sa := []int{1, 2, 3}
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i := 0
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i, sa[i] = 1, 2 // sets i = 1, sa[0] = 2
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sb := []int{1, 2, 3}
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j := 0
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sb[j], j = 2, 1 // sets sb[0] = 2, j = 1
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sc := []int{1, 2, 3}
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sc[0], sc[0] = 1, 2 // sets sc[0] = 1, then sc[0] = 2 (so sc[0] = 2 at end)
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</pre>
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<p>
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<em>Updating</em>:
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This is one change where tools cannot help, but breakage is unlikely.
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No code in the standard repository was broken by this change, and code
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that depended on the previous unspecified behavior was already incorrect.
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</p>
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<h3 id="shadowing">Returns and shadowed variables</h3>
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<p>
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A shadowed variable is one that has the same name as another variable in an inner scope.
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In functions with named return values,
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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.
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(It isn't part of the specification, because this is one area we are still exploring;
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the situation is analogous to the compilers rejecting functions that do not end with an explicit return statement.)
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</p>
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<p>
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This function implicitly returns a shadowed return value and will be rejected by the compiler:
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</p>
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<pre>
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func Bug() (i, j, k int) {
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for i = 0; i < 5; i++ {
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for j := 0; j < 5; j++ { // Redeclares j.
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k += i*j
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if k > 100 {
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return // Rejected: j is shadowed here.
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}
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}
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}
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return // OK: j is not shadowed here.
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}
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</pre>
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<p>
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<em>Updating</em>:
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Code that shadows return values in this way will be rejected by the compiler and will need to be fixed by hand.
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The few cases that arose in the standard repository were mostly bugs.
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</p>
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<h3 id="unexported">Copying structs with unexported fields</h3>
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<p>
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Go 1 relaxes the rules about accessing structs with unexported (lower-case) fields,
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permitting a client package to assign (and therefore copy) such a struct.
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Of course, the client package still cannot access such fields individually.
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</p>
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<p>
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As an example, if package <code>p</code> includes the definitions,
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</p>
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<pre>
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type Struct struct {
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Public int
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secret int
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}
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func NewStruct(a int) Struct { // Note: not a pointer.
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return Struct{a, f(a)}
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}
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func (s Struct) String() string {
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return fmt.Sprintf("{%d (secret %d)}", s.Public, s.secret)
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}
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</pre>
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<p>
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a package that imports <code>p</code> can assign and copy values of type
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<code>p.Struct</code> at will.
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Behind the scenes the unexported fields will be assigned and copied just
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as if they were exported,
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but the client code will never be aware of them. The code
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</p>
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<pre>
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import "p"
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myStruct := p.NewStruct(23)
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copyOfMyStruct := myStruct
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fmt.Println(myStruct, copyOfMyStruct)
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</pre>
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<p>
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will show that the secret field of the struct has been copied to the new value.
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</p>
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<p>
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<em>Updating</em>:
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This is a new feature, so existing code needs no changes.
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</p>
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<h3 id="equality">Equality of structs and arrays</h3>
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<p>
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Go 1 defines equality and inequality (<code>==</code> and
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<code>!=</code>) for struct and array values, respectively, provided
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the elements of the data structures can themselves be compared.
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That is, if equality is defined for all the fields of a struct (or
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an array element), then it is defined for the struct (or array).
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</p>
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<p>
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As a result, structs and arrays can now be used as map keys:
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</p>
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<pre><!--{{code "progs/go1.go" `/type Day struct/` `/Printf/`}}
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--> // type Day struct {
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// long string
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// short string
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// }
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// Christmas := Day{"Christmas", "XMas"}
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// Thanksgiving := Day{"Thanksgiving", "Turkey"}
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// holiday := map[Day]bool {
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// Christmas: true,
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// Thanksgiving: true,
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// }
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// fmt.Printf("Christmas is a holiday: %t\n", holiday[Christmas])
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</pre>
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<p>
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Note that equality is still undefined for slices, for which the
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calculation is in general infeasible. Also note that the ordered
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comparison operators (<code><</code> <code><=</code>
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<code>></code> <code>>=</code>) are still undefined for
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structs and arrays.
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<p>
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<em>Updating</em>:
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This is a new feature, so existing code needs no changes.
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</p>
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<h3 id="funcs">Function and map equality</h3>
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<p>
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Go 1 disallows checking for equality of functions and maps,
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respectively, except to compare them directly to <code>nil</code>.
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</p>
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<p>
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<em>Updating</em>:
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Existing code that depends on function or map equality will be
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rejected by the compiler and will need to be fixed by hand.
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Few programs will be affected, but the fix may require some
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redesign.
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</p>
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<h2 id="library">Changes to the library</h2>
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<h3 id="hierarchy">The package hierarchy</h3>
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<p>
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Go 1 has a rearranged package hierarchy that groups related items
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into subdirectories. For instance, <code>utf8</code> and
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<code>utf16</code> now occupy subdirectories of <code>unicode</code>.
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Also, <a href="#subrepo">some packages</a> have moved into
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subrepositories of
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<a href="http://code.google.com/p/go"><code>code.google.com/p/go</code></a>
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while <a href="#deleted">others</a> have been deleted outright.
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</p>
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<table class="codetable" frame="border" summary="Moved packages">
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<colgroup align="left" width="60%"></colgroup>
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<colgroup align="left" width="40%"></colgroup>
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<tr>
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<th align="left">Old path</th>
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<th align="left">New path</th>
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</tr>
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<tr><td>asn1</td> <td>encoding/asn1</td></tr>
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<tr><td>csv</td> <td>encoding/csv</td></tr>
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<tr><td>gob</td> <td>encoding/gob</td></tr>
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<tr><td>json</td> <td>encoding/json</td></tr>
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<tr><td>xml</td> <td>encoding/xml</td></tr>
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<tr>
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<td colspan="2"><hr></td>
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</tr>
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<tr><td>exp/template/html</td> <td>html/template</td></tr>
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<tr>
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<td colspan="2"><hr></td>
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</tr>
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<tr><td>big</td> <td>math/big</td></tr>
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<tr><td>cmath</td> <td>math/cmplx</td></tr>
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<tr><td>rand</td> <td>math/rand</td></tr>
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<tr>
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<td colspan="2"><hr></td>
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</tr>
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<tr><td>http</td> <td>net/http</td></tr>
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<tr><td>http/cgi</td> <td>net/http/cgi</td></tr>
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<tr><td>http/fcgi</td> <td>net/http/fcgi</td></tr>
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<tr><td>http/httptest</td> <td>net/http/httptest</td></tr>
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<tr><td>http/pprof</td> <td>net/http/pprof</td></tr>
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<tr><td>mail</td> <td>net/mail</td></tr>
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<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>:
|
|
Gofix 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.
|
|
<font color="red">TODO: should warn about deletions.</font>
|
|
<font color="red">TODO: should also handle packages that move to subrepos.</font>
|
|
</p>
|
|
|
|
<h3 id="errors">The error type</h3>
|
|
|
|
<h3 id="errno">System call errors</h3>
|
|
|
|
<h3 id="time">Time</h3>
|
|
|
|
<h3 id="html">The html package</h3>
|
|
|
|
<h3 id="http">The http package</h3>
|
|
|
|
<h3 id="strconv">The strconv package</h3>
|
|
|
|
<h3 id="exp">The package tree exp</h3>
|
|
|
|
<h3 id="old">The package tree old</h3>
|
|
|
|
<h3 id="deleted">Deleted packages</h3>
|
|
|
|
<!--
|
|
|
|
moving to exp/* (and thus not in Go 1):
|
|
ebnf, command ebnflint
|
|
go/types, command gotype
|
|
http/spdy
|
|
|
|
deleted:
|
|
container/vector
|
|
exp/datafmt
|
|
go/typechecker
|
|
try, command gotry
|
|
|
|
go/typechecker
|
|
go/types
|
|
ebnf (and cmd/ebnflint)
|
|
container/vector
|
|
try (and gotry)
|
|
exp/datafmt
|
|
netchan
|
|
-->
|
|
|
|
<h3 id="subrepo">Packages moving to subrepositories</h3>
|
|
|
|
<!--
|
|
crypto/openpgp to XXX
|
|
maybe exp/ssh?
|
|
-->
|
|
|
|
<h3 id="os_fileinfo">The os.FileInfo type</h3>
|
|
|
|
<h2 id="go_command">The go command</h2>
|
|
|
|
<h2 id="releases">Packaged releases</h2>
|
|
|