Initial commit: Go 1.23 release state

test/typeparam/settable.go

@@ -0,0 +1,123 @@
+// 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.
+
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+// Various implementations of fromStrings().
+
+type Setter[B any] interface {
+	Set(string)
+	*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"})
+}