提前感受下：Go 新泛型设计方案详解

func PrintSlice(type T)(s []T) {    for _, v := range s {        fmt.Printf("%v ", v)    }    fmt.Print("\n")}

// https://go2goplay.golang.org/p/rDbio9c4AQIpackage main
import "fmt"
func PrintSlice(type T)(s []T) {    for _, v := range s {        fmt.Printf("%v ", v)    }    fmt.Print("\n")}
func main() {    PrintSlice(int)([]int{1, 2, 3, 4, 5})    PrintSlice(float64)([]float64{1.01, 2.02, 3.03, 4.04, 5.05})    PrintSlice(string)([]string{"one", "two", "three", "four", "five"})}

1 2 3 4 5 1.01 2.02 3.03 4.04 5.05 one two three four five

// https://go2goplay.golang.org/p/UgHqZ7g4rbopackage main
import "fmt"
func PrintSlice(type T)(s []T) {    for _, v := range s {        fmt.Printf("%v ", v)    }    fmt.Print("\n")}
func main() {    PrintSlice([]int{1, 2, 3, 4, 5})    PrintSlice([]float64{1.01, 2.02, 3.03, 4.04, 5.05})    PrintSlice([]string{"one", "two", "three", "four", "five"})}

type Vector(type T) []T

//https://go2goplay.golang.org/p/tIZN2if1Wxo
package main
import "fmt"
func PrintSlice(type T)(s []T) {    for _, v := range s {        fmt.Printf("%v ", v)    }    fmt.Print("\n")}
type Vector(type T) []T
func main() {    var vs = Vector(int){1, 2, 3, 4, 5}    PrintSlice(vs)}

func main() {    var vs = Vector{1, 2, 3, 4, 5}    PrintSlice(vs)}

type checking failed for mainprog.go2:15:11: cannot use generic type Vector(type T) without instantiation

// https://go2goplay.golang.org/p/t0vXI6heUrTpackage main
import "fmt"
func Add(type T)(a, b T) T {    return a + b}
func main() {    c := Add(5, 6)    fmt.Println(c)}

type checking failed for mainprog.go2:6:9: invalid operation: operator + not defined for a (variable of type T)

// https://go2goplay.golang.org/p/kMxZI2vIsk-package main
import "fmt"
type PlusableInteger interface {    type int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64}
func Add(type T PlusableInteger)(a, b T) T {    return a + b}
func main() {    c := Add(5, 6)    fmt.Println(c)}

11

    f := Add(3.65, 7.23)    fmt.Println(f)

type checking failed for mainprog.go2:20:7: float64 does not satisfy PlusableInteger (float64 not found in int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64)

// https://go2goplay.golang.org/p/RchnTw73VMopackage main
type PlusableInteger interface {    type int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64}
func main() {    var n int = 6    var i PlusableInteger    i = n    _ = i}

type checking failed for mainprog.go2:9:8: interface type for variable cannot contain type constraints (int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64)

// https://go2goplay.golang.org/p/hyTbglTLoInpackage main
import (    "fmt"    "strconv")
type StringInt int
func (i StringInt) String() string {    return strconv.Itoa(int(i))}
type Stringer interface {    String() string}
func Stringify(type T Stringer)(s []T) (ret []string) {    for _, v := range s {        ret = append(ret, v.String())    }    return ret}
func main() {    fmt.Println(Stringify([]StringInt{1, 2, 3, 4, 5}))}

[1 2 3 4 5]

func main() {    fmt.Println(Stringify([]int{1, 2, 3, 4, 5}))}

type checking failed for mainprog.go2:27:2: int does not satisfy Stringer (missing method String)

// https://go2goplay.golang.org/p/tchwW6mPL7_dpackage main
import (    "fmt"    "strconv")
type StringInt int
func (i StringInt) String() string {    return strconv.Itoa(int(i))}
type SignedIntStringer interface {    type int, int8, int16, int32, int64    String() string}
func Stringify(type T SignedIntStringer)(s []T) (ret []string) {    for _, v := range s {        ret = append(ret, v.String())    }    return ret}
func main() {    fmt.Println(Stringify([]StringInt{1, 2, 3, 4, 5}))}

type StringInt uint

type checking failed for mainprog.go2:27:14: StringInt does not satisfy SignedIntStringer (uint not found in int, int8, int16, int32, int64)

// https://go2goplay.golang.org/p/tea39NqwZGCpackage main
import (    "fmt")
// Index returns the index of x in s, or -1 if not found.func Index(type T comparable)(s []T, x T) int {    for i, v := range s {        // v and x are type T, which has the comparable        // constraint, so we can use == here.        if v == x {            return i        }    }    return -1}
type Foo struct {    a string    b int}
func main() {    fmt.Println(Index([]int{1, 2, 3, 4, 5}, 3))    fmt.Println(Index([]string{"a", "b", "c", "d", "e"}, "d"))    pos := Index(        []Foo{            Foo{"a", 1},            Foo{"b", 2},            Foo{"c", 3},            Foo{"d", 4},            Foo{"e", 5},        }, Foo{"b", 2})    fmt.Println(pos)}

231

type ComparableStringer interface {    comparable    String() string}

// https://go2goplay.golang.org/p/O-YpTcW-tPu
// Package set implements sets of any comparable type.package main
// Set is a set of values.type Set(type T comparable) map[T]struct{}
// Make returns a set of some element type.func Make(type T comparable)() Set(T) {    return make(Set(T))}
// Add adds v to the set s.// If v is already in s this has no effect.func (s Set(T)) Add(v T) {    s[v] = struct{}{}}
// Delete removes v from the set s.// If v is not in s this has no effect.func (s Set(T)) Delete(v T) {    delete(s, v)}
// Contains reports whether v is in s.func (s Set(T)) Contains(v T) bool {    _, ok := s[v]    return ok}
// Len reports the number of elements in s.func (s Set(T)) Len() int {    return len(s)}
// Iterate invokes f on each element of s.// It's OK for f to call the Delete method.func (s Set(T)) Iterate(f func(T)) {    for v := range s {        f(v)    }}
func main() {    s := Make(int)()
    // Add the value 1,11,111 to the set s.    s.Add(1)    s.Add(11)    s.Add(111)
    // Check that s does not contain the value 11.    if s.Contains(11) {        println("the set contains 11")    }}

the set contains 11

// https://go2goplay.golang.org/p/JipsxG7jeCN
// Package set implements sets of any comparable type.package main
// Set is a set of values.type Set(type T comparable) map[T]struct{}
// Make returns a set of some element type.func Make(type T comparable)() Set(T) {    return make(Set(T))}
// Add adds v to the set s.// If v is already in s this has no effect.func (s Set(T)) Add(v T) {    s[v] = struct{}{}}
func (s Set(T)) Method1(type P)(v T, p P) {
}

func main() {    s := Make(int)()    s.Add(1)    s.Method1(10, 20)}

type checking failed for mainprog.go2:18:24: methods cannot have type parameters

type T Constraint

type *T Constraint

// https://go2goplay.golang.org/p/g3cwgguCmUopackage main
import (    "fmt"    "strconv")
type Setter interface {    Set(string)}
func FromStrings(type *T Setter)(s []string) []T {    result := make([]T, len(s))    for i, v := range s {        result[i].Set(v)    }    return result}
// Settable is a integer type that can be set from a string.type Settable int
// Set sets the value of *p from a string.func (p *Settable) Set(s string) {    i, _ := strconv.Atoi(s) // real code should not ignore the error    *p = Settable(i)}
func main() {    nums := FromStrings(Settable)([]string{"1", "2"})    fmt.Println(nums)}

[1 2]

type checking failed for mainprog.go2:30:22: Settable does not satisfy Setter (missing method Set)

We expect that most packages will not define generic types or functions, but many packages are likely to use generic types or functions defined elsewhere
我们期望大多数软件包不会定义泛型类型或函数，但是许多软件包可能会使用在其他地方定义的泛型类型或函数。