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