+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. +
+ + type Date struct {
+ month string
+ day int
+ }
+ // Struct values, fully qualified; always legal.
+ holiday1 := []Date{
+ Date{"Feb", 14},
+ Date{"Nov", 11},
+ Date{"Dec", 25},
+ }
+ // Struct values, type name elided; always legal.
+ holiday2 := []Date{
+ {"Feb", 14},
+ {"Nov", 11},
+ {"Dec", 25},
+ }
+ // Pointers, fully qualified, always legal.
+ holiday3 := []*Date{
+ &Date{"Feb", 14},
+ &Date{"Nov", 11},
+ &Date{"Dec", 25},
+ }
+ // Pointers, type name elided; legal in Go 1.
+ holiday4 := []*Date{
+ {"Feb", 14},
+ {"Nov", 11},
+ {"Dec", 25},
+ }
+
+
+
+Updating:
+This change has no effect on existing code, but the command
+gofmt -s applied to existing source
+will, among other things, elide explicit element types wherever permitted.
+
@@ -119,6 +164,62 @@ There was no such code in the standard repository.
+Go 1 introduces a new basic type, rune, to be used to represent
+individual Unicode code points.
+It is an alias for int32, analogous to byte
+as an alias for uint8.
+
+Character literals such as 'a', '語', and '\u0345'
+now have default type rune,
+analogous to 1.0 having default type float64.
+A variable initialized to a character constant will therefore
+have type rune unless otherwise specified.
+
+Libraries have been updated to use rune rather than int
+when appropriate. For instance, the functions unicode.ToLower and
+relatives now take and return a rune.
+
delta := 'δ' // delta has type rune.
+ var DELTA rune
+ DELTA = unicode.ToUpper(delta)
+ epsilon := unicode.ToLower(DELTA + 1)
+ if epsilon != 'δ'+1 {
+ log.Fatal("inconsistent casing for Greek")
+ }
+
+
+
+Updating:
+Most source code will be unaffected by this because the type inference from
+:= initializers introduces the new type silently, and it propagates
+from there.
+Some code may get type errors that a trivial conversion will resolve.
+
+Go 1 introduces a new built-in type, error, which has the following definition:
+
+ type error interface {
+ Error() string
+ }
+
+
++Since the consequences of this type are all in the package library, +it is discussed below. +
+@@ -126,7 +227,7 @@ The original syntax for deleting an element in a map was:
- m[x] = ignored, false + m[k] = ignored, false
@@ -210,6 +311,7 @@ These examples illustrate the behavior. sc[0], sc[0] = 1, 2 // sets sc[0] = 1, then sc[0] = 2 (so sc[0] = 2 at end) +
Updating: 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 @@ -252,6 +354,54 @@ The few cases that arose in the standard repository were mostly bugs.
+Go 1 relaxes the rules about accessing structs with unexported (lower-case) fields, +permitting a client package to assign (and therefore copy) such a struct. +Of course, the client package still cannot access such fields individually. +
+ +
+As an example, if package p includes the definitions,
+
+ 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)
+ }
+
+
+
+a package that imports p can assign and copy values of type
+p.Struct 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
+
+ import "p" + + myStruct := p.NewStruct(23) + copyOfMyStruct := myStruct + fmt.Println(myStruct, copyOfMyStruct) ++ +
+will show that the secret field of the struct has been copied to the new value. +
+ ++Updating: +This is a new feature, so existing code needs no changes. +
+diff --git a/doc/go1.tmpl b/doc/go1.tmpl index d317f3b0f0..04e72dfab2 100644 --- a/doc/go1.tmpl +++ b/doc/go1.tmpl @@ -81,6 +81,22 @@ now reject such code.
+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. +
+ +{{code "progs/go1.go" `/type Date struct/` `/STOP/`}} + +
+Updating:
+This change has no effect on existing code, but the command
+gofmt -s applied to existing source
+will, among other things, elide explicit element types wherever permitted.
+
@@ -102,6 +118,54 @@ There was no such code in the standard repository.
+Go 1 introduces a new basic type, rune, to be used to represent
+individual Unicode code points.
+It is an alias for int32, analogous to byte
+as an alias for uint8.
+
+Character literals such as 'a', '語', and '\u0345'
+now have default type rune,
+analogous to 1.0 having default type float64.
+A variable initialized to a character constant will therefore
+have type rune unless otherwise specified.
+
+Libraries have been updated to use rune rather than int
+when appropriate. For instance, the functions unicode.ToLower and
+relatives now take and return a rune.
+
+Updating:
+Most source code will be unaffected by this because the type inference from
+:= initializers introduces the new type silently, and it propagates
+from there.
+Some code may get type errors that a trivial conversion will resolve.
+
+Go 1 introduces a new built-in type, error, which has the following definition:
+
+ type error interface {
+ Error() string
+ }
+
+
++Since the consequences of this type are all in the package library, +it is discussed below. +
+@@ -109,7 +173,7 @@ The original syntax for deleting an element in a map was:
- m[x] = ignored, false + m[k] = ignored, false
@@ -174,6 +238,7 @@ These examples illustrate the behavior. {{code "progs/go1.go" `/sa :=/` `/then sc.0. = 2/`}} +
Updating: 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 @@ -216,6 +281,54 @@ The few cases that arose in the standard repository were mostly bugs.
+Go 1 relaxes the rules about accessing structs with unexported (lower-case) fields, +permitting a client package to assign (and therefore copy) such a struct. +Of course, the client package still cannot access such fields individually. +
+ +
+As an example, if package p includes the definitions,
+
+ 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)
+ }
+
+
+
+a package that imports p can assign and copy values of type
+p.Struct 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
+
+ import "p" + + myStruct := p.NewStruct(23) + copyOfMyStruct := myStruct + fmt.Println(myStruct, copyOfMyStruct) ++ +
+will show that the secret field of the struct has been copied to the new value. +
+ ++Updating: +This is a new feature, so existing code needs no changes. +
+diff --git a/doc/progs/go1.go b/doc/progs/go1.go index f02ede7403..caceb0513c 100644 --- a/doc/progs/go1.go +++ b/doc/progs/go1.go @@ -6,7 +6,10 @@ package main -import "log" +import ( + "log" + "unicode" +) func main() { stringAppend() @@ -14,6 +17,8 @@ func main() { mapIteration() multipleAssignment() structEquality() + compositeLiterals() + runeType() } func mapDelete() { @@ -80,6 +85,51 @@ func structEquality() { // fmt.Printf("Christmas is a holiday: %t\n", holiday[Christmas]) } +func compositeLiterals() { + type Date struct { + month string + day int + } + // Struct values, fully qualified; always legal. + holiday1 := []Date{ + Date{"Feb", 14}, + Date{"Nov", 11}, + Date{"Dec", 25}, + } + // Struct values, type name elided; always legal. + holiday2 := []Date{ + {"Feb", 14}, + {"Nov", 11}, + {"Dec", 25}, + } + // Pointers, fully qualified, always legal. + holiday3 := []*Date{ + &Date{"Feb", 14}, + &Date{"Nov", 11}, + &Date{"Dec", 25}, + } + // Pointers, type name elided; legal in Go 1. + holiday4 := []*Date{ + {"Feb", 14}, + {"Nov", 11}, + {"Dec", 25}, + } + // STOP OMIT + _, _, _, _ = holiday1, holiday2, holiday3, holiday4 +} + +func runeType() { + // STARTRUNE OMIT + delta := 'δ' // delta has type rune. + var DELTA rune + DELTA = unicode.ToUpper(delta) + epsilon := unicode.ToLower(DELTA + 1) + if epsilon != 'δ'+1 { + log.Fatal("inconsistent casing for Greek") + } + // ENDRUNE OMIT +} + func f(string, int) { }