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 implement 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 implement int" */ ]]() {}
37
38 // Additional tests
39 func _[P T[T /* ERROR "T\[P\] does not implement int" */ [P /* ERROR "P does not implement int" */ ]]]() {}
40 func _[P T[Q /* ERROR "Q does not implement int" */ ], Q T[P /* ERROR "P does not implement 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 implement comparable" */ [Q /* ERROR "Q does not implement comparable" */]], Q func()]() {}
46 func _[P [10]C[P]]() {}
47 func _[P struct{ f C[C[P]]}]() {}
48
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