| // run |
| |
| // Copyright 2020 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 |
| |
| type Gen[A any] func() (A, bool) |
| |
| func combine[T1, T2, T any](g1 Gen[T1], g2 Gen[T2], join func(T1, T2) T) Gen[T] { |
| return func() (T, bool) { |
| var t T |
| t1, ok := g1() |
| if !ok { |
| return t, false |
| } |
| t2, ok := g2() |
| if !ok { |
| return t, false |
| } |
| return join(t1, t2), true |
| } |
| } |
| |
| type Pair[A, B any] struct { |
| A A |
| B B |
| } |
| |
| func NewPair[A, B any](a A, b B) Pair[A, B] { return Pair[A, B]{a, b} } |
| |
| func Combine2[A, B any](ga Gen[A], gb Gen[B]) Gen[Pair[A, B]] { |
| return combine(ga, gb, NewPair(A, B)) |
| } |
| |
| func main() { |
| var g1 Gen[int] = func() (int, bool) { return 3, true } |
| var g2 Gen[string] = func() (string, bool) { return "x", false } |
| gc := combine(g1, g2, NewPair[int, string]) |
| gc2 := Combine2(g1, g2) |
| if got, ok := gc(); ok { |
| panic(got) |
| } |
| if got2, ok := gc2(); ok { |
| panic(got2) |
| } |
| } |