mirror of
https://github.com/golang/go
synced 2024-11-02 13:42:29 +00:00
5355753009
We don't usually reformat the test directory, but all of the files in test/typeparam are syntactically valid. I suspect the misformattings here are because developers aren't re-installing gofmt with -tags=typeparams, not intentionally exercising non-standard formatting. Change-Id: I3767d480434c19225568f3c7d656dc8589197183 Reviewed-on: https://go-review.googlesource.com/c/go/+/338093 Trust: Matthew Dempsky <mdempsky@google.com> Trust: Robert Griesemer <gri@golang.org> Run-TryBot: Matthew Dempsky <mdempsky@google.com> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@golang.org>
123 lines
2.8 KiB
Go
123 lines
2.8 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.
|
|
|
|
package main
|
|
|
|
import (
|
|
"fmt"
|
|
"strconv"
|
|
)
|
|
|
|
// Various implementations of fromStrings().
|
|
|
|
type Setter[B any] interface {
|
|
Set(string)
|
|
type *B
|
|
}
|
|
|
|
// Takes two type parameters where PT = *T
|
|
func fromStrings1[T any, PT Setter[T]](s []string) []T {
|
|
result := make([]T, len(s))
|
|
for i, v := range s {
|
|
// The type of &result[i] is *T which is in the type list
|
|
// of Setter, so we can convert it to PT.
|
|
p := PT(&result[i])
|
|
// PT has a Set method.
|
|
p.Set(v)
|
|
}
|
|
return result
|
|
}
|
|
|
|
func fromStrings1a[T any, PT Setter[T]](s []string) []PT {
|
|
result := make([]PT, len(s))
|
|
for i, v := range s {
|
|
// The type new(T) is *T which is in the type list
|
|
// of Setter, so we can convert it to PT.
|
|
result[i] = PT(new(T))
|
|
p := result[i]
|
|
// PT has a Set method.
|
|
p.Set(v)
|
|
}
|
|
return result
|
|
}
|
|
|
|
// Takes one type parameter and a set function
|
|
func fromStrings2[T any](s []string, set func(*T, string)) []T {
|
|
results := make([]T, len(s))
|
|
for i, v := range s {
|
|
set(&results[i], v)
|
|
}
|
|
return results
|
|
}
|
|
|
|
type Setter2 interface {
|
|
Set(string)
|
|
}
|
|
|
|
// Takes only one type parameter, but causes a panic (see below)
|
|
func fromStrings3[T Setter2](s []string) []T {
|
|
results := make([]T, len(s))
|
|
for i, v := range s {
|
|
// Panics if T is a pointer type because receiver is T(nil).
|
|
results[i].Set(v)
|
|
}
|
|
return results
|
|
}
|
|
|
|
// Two concrete types with the appropriate Set method.
|
|
|
|
type SettableInt int
|
|
|
|
func (p *SettableInt) Set(s string) {
|
|
i, err := strconv.Atoi(s)
|
|
if err != nil {
|
|
panic(err)
|
|
}
|
|
*p = SettableInt(i)
|
|
}
|
|
|
|
type SettableString struct {
|
|
s string
|
|
}
|
|
|
|
func (x *SettableString) Set(s string) {
|
|
x.s = s
|
|
}
|
|
|
|
func main() {
|
|
s := fromStrings1[SettableInt, *SettableInt]([]string{"1"})
|
|
if len(s) != 1 || s[0] != 1 {
|
|
panic(fmt.Sprintf("got %v, want %v", s, []int{1}))
|
|
}
|
|
|
|
s2 := fromStrings1a[SettableInt, *SettableInt]([]string{"1"})
|
|
if len(s2) != 1 || *s2[0] != 1 {
|
|
x := 1
|
|
panic(fmt.Sprintf("got %v, want %v", s2, []*int{&x}))
|
|
}
|
|
|
|
// Test out constraint type inference, which should determine that the second
|
|
// type param is *SettableString.
|
|
ps := fromStrings1[SettableString]([]string{"x", "y"})
|
|
if len(ps) != 2 || ps[0] != (SettableString{"x"}) || ps[1] != (SettableString{"y"}) {
|
|
panic(s)
|
|
}
|
|
|
|
s = fromStrings2([]string{"1"}, func(p *SettableInt, s string) { p.Set(s) })
|
|
if len(s) != 1 || s[0] != 1 {
|
|
panic(fmt.Sprintf("got %v, want %v", s, []int{1}))
|
|
}
|
|
|
|
defer func() {
|
|
if recover() == nil {
|
|
panic("did not panic as expected")
|
|
}
|
|
}()
|
|
// This should type check but should panic at run time,
|
|
// because it will make a slice of *SettableInt and then call
|
|
// Set on a nil value.
|
|
fromStrings3[*SettableInt]([]string{"1"})
|
|
}
|