Text file src/go/types/testdata/check/typeinst.go2

     1  // Copyright 2019 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  type myInt int
     8  
     9  // Parameterized type declarations
    10  
    11  // For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
    12  type T1[P any] P // ERROR cannot use a type parameter as RHS in type declaration
    13  
    14  type T2[P any] struct {
    15          f P
    16          g int // int should still be in scope chain
    17  }
    18  
    19  type List[P any] []P
    20  
    21  // Alias type declarations cannot have type parameters.
    22  // Issue #46477 proposses to change that.
    23  type A1[P any] = /* ERROR cannot be alias */ struct{}
    24  
    25  // Pending clarification of #46477 we disallow aliases
    26  // of generic types.
    27  type A2 = List // ERROR cannot use generic type
    28  var _ A2[int]
    29  var _ A2
    30  
    31  type A3 = List[int]
    32  var _ A3
    33  
    34  // Parameterized type instantiations
    35  
    36  var x int
    37  type _ x /* ERROR not a type */ [int]
    38  
    39  type _ int /* ERROR not a generic type */ [] // ERROR expected type argument list
    40  type _ myInt /* ERROR not a generic type */ [] // ERROR expected type argument list
    41  
    42  // TODO(gri) better error messages
    43  type _ T1[] // ERROR expected type argument list
    44  type _ T1[x /* ERROR not a type */ ]
    45  type _ T1 /* ERROR got 2 arguments but 1 type parameters */ [int, float32]
    46  
    47  var _ T2[int] = T2[int]{}
    48  
    49  var _ List[int] = []int{1, 2, 3}
    50  var _ List[[]int] = [][]int{{1, 2, 3}}
    51  var _ List[List[List[int]]]
    52  
    53  // Parameterized types containing parameterized types
    54  
    55  type T3[P any] List[P]
    56  
    57  var _ T3[int] = T3[int](List[int]{1, 2, 3})
    58  
    59  // Self-recursive generic types are not permitted
    60  
    61  type self1[P any] self1 /* ERROR illegal cycle */ [P]
    62  type self2[P any] *self2[P] // this is ok
    63  

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