test/typeparam/typelist.go

// compile -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 file tests type lists & structural constraints.

package p

// Assignability of an unnamed pointer type to a type parameter that
// has a matching underlying type.
func _[T interface{}, PT interface{ type *T }](x T) PT {
	return &x
}

// Indexing of generic types containing type parameters in their type list:
func at[T interface{ type []E }, E any](x T, i int) E {
	return x[i]
}

// A generic type inside a function acts like a named type. Its underlying
// type is itself, its "operational type" is defined by the type list in
// the tybe bound, if any.
func _[T interface{ type int }](x T) {
	type myint int
	var _ int = int(x)
	var _ T = 42
	var _ T = T(myint(42))
}

// Indexing a generic type which has a structural contraints to be an array.
func _[T interface{ type [10]int }](x T) {
	_ = x[9] // ok
}

// Dereference of a generic type which has a structural contraint to be a pointer.
func _[T interface{ type *int }](p T) int {
	return *p
}

// Channel send and receive on a generic type which has a structural constraint to
// be a channel.
func _[T interface{ type chan int }](ch T) int {
	// This would deadlock if executed (but ok for a compile test)
	ch <- 0
	return <-ch
}

// Calling of a generic type which has a structural constraint to be a function.
func _[T interface{ type func() }](f T) {
	f()
	go f()
}

// Same, but function has a parameter and return value.
func _[T interface{ type func(string) int }](f T) int {
	return f("hello")
}

// Map access of a generic type which has a structural constraint to be a map.
func _[V any, T interface{ type map[string]V }](p T) V {
	return p["test"]
}

// Testing partial and full type inference, including the case where the types can
// be inferred without needing the types of the function arguments.

// Cannot embed stand-alone type parameters. Disabled for now.
/*
func f0[A any, B interface{type C}, C interface{type D}, D interface{type A}](A, B, C, D)
func f0x() {
        f := f0[string]
        f("a", "b", "c", "d")
        f0("a", "b", "c", "d")
}

func f1[A any, B interface{type A}](A, B)
func f1x() {
        f := f1[int]
        f(int(0), int(0))
        f1(int(0), int(0))
        f(0, 0)
        f1(0, 0)
}
*/

func f2[A any, B interface{ type []A }](_ A, _ B) {}
func f2x() {
	f := f2[byte]
	f(byte(0), []byte{})
	f2(byte(0), []byte{})
	f(0, []byte{})
	// f2(0, []byte{}) - this one doesn't work
}

// Cannot embed stand-alone type parameters. Disabled for now.
/*
func f3[A any, B interface{type C}, C interface{type *A}](a A, _ B, c C)
func f3x() {
	f := f3[int]
	var x int
	f(x, &x, &x)
	f3(x, &x, &x)
}
*/

func f4[A any, B interface{ type []C }, C interface{ type *A }](_ A, _ B, c C) {}
func f4x() {
	f := f4[int]
	var x int
	f(x, []*int{}, &x)
	f4(x, []*int{}, &x)
}

func f5[A interface {
	type struct {
		b B
		c C
	}
}, B any, C interface{ type *B }](x B) A { panic(0) }
func f5x() {
	x := f5(1.2)
	var _ float64 = x.b
	var _ float64 = *x.c
}

func f6[A any, B interface{ type struct{ f []A } }](B) A { panic(0) }
func f6x() {
	x := f6(struct{ f []string }{})
	var _ string = x
}