mirror of
https://github.com/golang/go
synced 2024-09-15 22:20:06 +00:00
doc/go1: the rest of the language changes
R=rsc CC=golang-dev https://golang.org/cl/5478047
This commit is contained in:
Rob Pike
parent
940c25faa4
commit
2e338fa69f
152
doc/go1.html
152
doc/go1.html
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@ -90,6 +90,51 @@ now reject such code.
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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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@ -119,6 +164,62 @@ There was no such code in the standard repository.
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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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@ -126,7 +227,7 @@ 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[x] = ignored, false
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m[k] = ignored, false
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</pre>
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<p>
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@ -210,6 +311,7 @@ These examples illustrate the behavior.
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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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@ -252,6 +354,54 @@ The few cases that arose in the standard repository were mostly bugs.
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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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115
doc/go1.tmpl
115
doc/go1.tmpl
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@ -81,6 +81,22 @@ now reject such code.
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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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{{code "progs/go1.go" `/type Date struct/` `/STOP/`}}
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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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@ -102,6 +118,54 @@ There was no such code in the standard repository.
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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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{{code "progs/go1.go" `/STARTRUNE/` `/ENDRUNE/`}}
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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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@ -109,7 +173,7 @@ 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[x] = ignored, false
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m[k] = ignored, false
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</pre>
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<p>
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@ -174,6 +238,7 @@ These examples illustrate the behavior.
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{{code "progs/go1.go" `/sa :=/` `/then sc.0. = 2/`}}
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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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@ -216,6 +281,54 @@ The few cases that arose in the standard repository were mostly bugs.
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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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@ -6,7 +6,10 @@
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package main
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import "log"
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import (
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"log"
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"unicode"
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)
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func main() {
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stringAppend()
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@ -14,6 +17,8 @@ func main() {
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mapIteration()
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multipleAssignment()
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structEquality()
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compositeLiterals()
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runeType()
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}
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func mapDelete() {
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@ -80,6 +85,51 @@ func structEquality() {
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// fmt.Printf("Christmas is a holiday: %t\n", holiday[Christmas])
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}
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func compositeLiterals() {
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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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// STOP OMIT
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_, _, _, _ = holiday1, holiday2, holiday3, holiday4
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}
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func runeType() {
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// STARTRUNE OMIT
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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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// ENDRUNE OMIT
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}
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func f(string, int) {
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}
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|
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Reference in a new issue