issue50782.go

     1  // Copyright 2022 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  // Field accesses through type parameters are disabled
     6  // until we have a more thorough understanding of the
     7  // implications on the spec. See issue #51576.
     8  
     9  package p
    10  
    11  // The first example from the issue.
    12  type Numeric interface {
    13  	~int | ~int8 | ~int16 | ~int32 | ~int64
    14  }
    15  
    16  // numericAbs matches numeric types with an Abs method.
    17  type numericAbs[T Numeric] interface {
    18  	~struct{ Value T }
    19  	Abs() T
    20  }
    21  
    22  // AbsDifference computes the absolute value of the difference of
    23  // a and b, where the absolute value is determined by the Abs method.
    24  func absDifference[T numericAbs[T /* ERROR "T does not satisfy Numeric" */]](a, b T) T {
    25  	// Field accesses are not permitted for now. Keep an error so
    26  	// we can find and fix this code once the situation changes.
    27  	return a.Value // ERROR "a.Value undefined"
    28  	// TODO: The error below should probably be positioned on the '-'.
    29  	// d := a /* ERROR "invalid operation: operator - not defined" */ .Value - b.Value
    30  	// return d.Abs()
    31  }
    32  
    33  // The second example from the issue.
    34  type T[P int] struct{ f P }
    35  
    36  func _[P T[P /* ERROR "P does not satisfy int" */ ]]() {}
    37  
    38  // Additional tests
    39  func _[P T[T /* ERROR "T[P] does not satisfy int" */ [P /* ERROR "P does not satisfy int" */ ]]]() {}
    40  func _[P T[Q /* ERROR "Q does not satisfy int" */ ], Q T[P /* ERROR "P does not satisfy int" */ ]]() {}
    41  func _[P T[Q], Q int]() {}
    42  
    43  type C[P comparable] struct{ f P }
    44  func _[P C[C[P]]]() {}
    45  func _[P C[C /* ERROR "C[Q] does not satisfy comparable" */ [Q /* ERROR "Q does not satisfy comparable" */]], Q func()]() {}
    46  func _[P [10]C[P]]() {}
    47  func _[P struct{ f C[C[P]]}]() {}
    48
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