typeinst0.go

     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  // Pending clarification of #46477 we disallow aliases
    22  // of generic types.
    23  type A2 = List // ERROR "cannot use generic type"
    24  var _ A2[int]
    25  var _ A2
    26  
    27  type A3 = List[int]
    28  var _ A3
    29  
    30  // Parameterized type instantiations
    31  
    32  var x int
    33  type _ x /* ERROR "not a type" */ [int]
    34  
    35  type _ int /* ERROR "not a generic type" */ [] // ERROR "expected type argument list"
    36  type _ myInt /* ERROR "not a generic type" */ [] // ERROR "expected type argument list"
    37  
    38  // TODO(gri) better error messages
    39  type _ T1[] // ERROR "expected type argument list"
    40  type _ T1[x /* ERROR "not a type" */ ]
    41  type _ T1 /* ERROR "too many type arguments for type T1: have 2, want 1" */ [int, float32]
    42  
    43  var _ T2[int] = T2[int]{}
    44  
    45  var _ List[int] = []int{1, 2, 3}
    46  var _ List[[]int] = [][]int{{1, 2, 3}}
    47  var _ List[List[List[int]]]
    48  
    49  // Parameterized types containing parameterized types
    50  
    51  type T3[P any] List[P]
    52  
    53  var _ T3[int] = T3[int](List[int]{1, 2, 3})
    54  
    55  // Self-recursive generic types are not permitted
    56  
    57  type self1[P any] self1 /* ERROR "invalid recursive type" */ [P]
    58  type self2[P any] *self2[P] // this is ok
    59
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