| // 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 p | |
| type Optional[T any] struct {} | |
| func (_ Optional[T]) Val() (T, bool) | |
| type Box[T any] interface { | |
| Val() (T, bool) | |
| } | |
| func f[V interface{}, A, B Box[V]]() {} | |
| func _() { | |
| f[int, Optional[int], Optional[int]]() | |
| // f[int, Optional[int], Optional /* ERROR does not satisfy Box */ [string]]() | |
| } |