dottype.go

     1  // run
     2  
     3  // Copyright 2021 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  package main
     8  
     9  func f[T any](x interface{}) T {
    10  	return x.(T)
    11  }
    12  func f2[T any](x interface{}) (T, bool) {
    13  	t, ok := x.(T)
    14  	return t, ok
    15  }
    16  
    17  type I interface {
    18  	foo()
    19  }
    20  
    21  type myint int
    22  
    23  func (myint) foo() {
    24  }
    25  
    26  type myfloat float64
    27  
    28  func (myfloat) foo() {
    29  }
    30  
    31  func g[T I](x I) T {
    32  	return x.(T)
    33  }
    34  func g2[T I](x I) (T, bool) {
    35  	t, ok := x.(T)
    36  	return t, ok
    37  }
    38  
    39  func h[T any](x interface{}) struct{ a, b T } {
    40  	return x.(struct{ a, b T })
    41  }
    42  
    43  func k[T any](x interface{}) interface{ bar() T } {
    44  	return x.(interface{ bar() T })
    45  }
    46  
    47  type mybar int
    48  
    49  func (x mybar) bar() int {
    50  	return int(x)
    51  }
    52  
    53  func main() {
    54  	var i interface{} = int(3)
    55  	var j I = myint(3)
    56  	var x interface{} = float64(3)
    57  	var y I = myfloat(3)
    58  
    59  	println(f[int](i))
    60  	shouldpanic(func() { f[int](x) })
    61  	println(f2[int](i))
    62  	println(f2[int](x))
    63  
    64  	println(g[myint](j))
    65  	shouldpanic(func() { g[myint](y) })
    66  	println(g2[myint](j))
    67  	println(g2[myint](y))
    68  
    69  	println(h[int](struct{ a, b int }{3, 5}).a)
    70  
    71  	println(k[int](mybar(3)).bar())
    72  
    73  	type large struct {a,b,c,d,e,f int}
    74  	println(f[large](large{}).a)
    75  	l2, ok := f2[large](large{})
    76  	println(l2.a, ok)
    77  }
    78  func shouldpanic(x func()) {
    79  	defer func() {
    80  		e := recover()
    81  		if e == nil {
    82  			panic("didn't panic")
    83  		}
    84  	}()
    85  	x()
    86  }
    87
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