mirror of
https://github.com/golang/go
synced 2024-11-18 03:34:42 -07:00
a91d0b649c
We may revisit this decision in a future release. By disallowing this for Go 1.18 we are ensuring that we don't lock in the generics design in a place that may need to change later. (Type declarations are the primary construct where it crucially matters what the underlying type of a type parameter is.) Comment out all tests that rely on this feature; add comments referring to issue so we can find all places easily should we change our minds. Fixes #45639. Change-Id: I730510e4da66d3716d455a9071c7778a1e4a1152 Reviewed-on: https://go-review.googlesource.com/c/go/+/359177 Trust: Robert Griesemer <gri@golang.org> Trust: Dan Scales <danscales@google.com> Reviewed-by: Dan Scales <danscales@google.com>
109 lines
2.7 KiB
Go
109 lines
2.7 KiB
Go
// run -gcflags=-G=3
|
|
|
|
// 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 a 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))
|
|
}
|
|
}
|