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// 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.
// Test for cases where certain instantiations of a generic function (F in this
// example) will always fail on a type assertion or mismatch on a type case.
package main
import "fmt"
type S struct{}
func (S) M() byte {
return 0
}
type I[T any] interface {
M() T
}
func F[T, A any](x I[T], shouldMatch bool) {
switch x.(type) {
case A:
if !shouldMatch {
fmt.Printf("wanted mis-match, got match")
}
default:
if shouldMatch {
fmt.Printf("wanted match, got mismatch")
}
}
_, ok := x.(A)
if ok != shouldMatch {
fmt.Printf("ok: got %v, wanted %v", ok, shouldMatch)
}
if !shouldMatch {
defer func() {
if shouldMatch {
fmt.Printf("Shouldn't have panicked")
}
recover()
}()
}
_ = x.(A)
if !shouldMatch {
fmt.Printf("Should have panicked")
}
}
func main() {
// Test instantiation where the type switch/type asserts can't possibly succeed
// (since string does not implement I[byte]).
F[byte, string](S{}, false)
// Test instantiation where the type switch/type asserts should succeed
// (since S does implement I[byte])
F[byte, S](S{}, true)
F[byte, S](I[byte](S{}), true)
}
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