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// run
// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// This test illustrates how a type bound method (String below) can be implemented
// either by a concrete type (myint below) or an instantiated generic type
// (StringInt[myint] below).
package main
import (
"fmt"
"reflect"
"strconv"
)
type myint int
//go:noinline
func (m myint) String() string {
return strconv.Itoa(int(m))
}
type Stringer interface {
String() string
}
func stringify[T Stringer](s []T) (ret []string) {
for _, v := range s {
// Test normal bounds method call on type param
x1 := v.String()
// Test converting type param to its bound interface first
v1 := Stringer(v)
x2 := v1.String()
// Test method expression with type param type
f1 := T.String
x3 := f1(v)
// Test creating and calling closure equivalent to the method expression
f2 := func(v1 T) string {
return Stringer(v1).String()
}
x4 := f2(v)
if x1 != x2 || x2 != x3 || x3 != x4 {
panic(fmt.Sprintf("Mismatched values %v, %v, %v, %v\n", x1, x2, x3, x4))
}
ret = append(ret, v.String())
}
return ret
}
type Ints interface {
~int32 | ~int
}
// For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
// type StringInt[T Ints] T
//
// //go:noinline
// func (m StringInt[T]) String() string {
// return strconv.Itoa(int(m))
// }
type StringStruct[T Ints] struct {
f T
}
func (m StringStruct[T]) String() string {
return strconv.Itoa(int(m.f))
}
func main() {
x := []myint{myint(1), myint(2), myint(3)}
// stringify on a normal type, whose bound method is associated with the base type.
got := stringify(x)
want := []string{"1", "2", "3"}
if !reflect.DeepEqual(got, want) {
panic(fmt.Sprintf("got %s, want %s", got, want))
}
// For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
// x2 := []StringInt[myint]{StringInt[myint](5), StringInt[myint](7), StringInt[myint](6)}
//
// // stringify on an instantiated type, whose bound method is associated with
// // the generic type StringInt[T], which maps directly to T.
// got2 := stringify(x2)
// want2 := []string{"5", "7", "6"}
// if !reflect.DeepEqual(got2, want2) {
// panic(fmt.Sprintf("got %s, want %s", got2, want2))
// }
// stringify on an instantiated type, whose bound method is associated with
// the generic type StringStruct[T], which maps to a struct containing T.
x3 := []StringStruct[myint]{StringStruct[myint]{f: 11}, StringStruct[myint]{f: 10}, StringStruct[myint]{f: 9}}
got3 := stringify(x3)
want3 := []string{"11", "10", "9"}
if !reflect.DeepEqual(got3, want3) {
panic(fmt.Sprintf("got %s, want %s", got3, want3))
}
}