issue47747.go

     1  // Copyright 2021 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package p
     6  
     7  // For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
     8  // type T1[P any] P
     9  // 
    10  // func (T1[_]) m() {}
    11  // 
    12  // func _[P any](x *T1[P]) {
    13  //         // x.m exists because x is of type *T1 where T1 is a defined type
    14  //         // (even though under(T1) is a type parameter)
    15  //         x.m()
    16  // }
    17  
    18  
    19  func _[P interface{ m() }](x P) {
    20          x.m()
    21          // (&x).m doesn't exist because &x is of type *P
    22          // and pointers to type parameters don't have methods
    23          (&x).m /* ERROR "type *P is pointer to type parameter, not type parameter" */ ()
    24  }
    25  
    26  
    27  type T2 interface{ m() }
    28  
    29  func _(x *T2) {
    30          // x.m doesn't exists because x is of type *T2
    31          // and pointers to interfaces don't have methods
    32          x.m /* ERROR "type *T2 is pointer to interface, not interface" */()
    33  }
    34  
    35  // Test case 1 from issue
    36  
    37  type Fooer1[t any] interface {
    38  	Foo(Barer[t])
    39  }
    40  type Barer[t any] interface {
    41  	Bar(t)
    42  }
    43  
    44  // For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
    45  // type Foo1[t any] t
    46  // type Bar[t any] t
    47  // 
    48  // func (l Foo1[t]) Foo(v Barer[t]) { v.Bar(t(l)) }
    49  // func (b *Bar[t]) Bar(l t)        { *b = Bar[t](l) }
    50  // 
    51  // func _[t any](f Fooer1[t]) t {
    52  // 	var b Bar[t]
    53  // 	f.Foo(&b)
    54  // 	return t(b)
    55  // }
    56  
    57  // Test case 2 from issue
    58  
    59  // For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
    60  // type Fooer2[t any] interface {
    61  // 	Foo()
    62  // }
    63  // 
    64  // type Foo2[t any] t
    65  // 
    66  // func (f *Foo2[t]) Foo() {}
    67  // 
    68  // func _[t any](v t) {
    69  // 	var f = Foo2[t](v)
    70  // 	_ = Fooer2[t](&f)
    71  // }
    72
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