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Diffstat (limited to 'src/internal/types/testdata/examples/constraints.go')
-rw-r--r-- | src/internal/types/testdata/examples/constraints.go | 80 |
1 files changed, 80 insertions, 0 deletions
diff --git a/src/internal/types/testdata/examples/constraints.go b/src/internal/types/testdata/examples/constraints.go new file mode 100644 index 0000000..5b14489 --- /dev/null +++ b/src/internal/types/testdata/examples/constraints.go @@ -0,0 +1,80 @@ +// Copyright 2021 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// This file shows some examples of generic constraint interfaces. + +package p + +type MyInt int + +type ( + // Arbitrary types may be embedded like interfaces. + _ interface{int} + _ interface{~int} + + // Types may be combined into a union. + union interface{int|~string} + + // Union terms must describe disjoint (non-overlapping) type sets. + _ interface{int|int /* ERROR overlapping terms int */ } + _ interface{int|~ /* ERROR overlapping terms ~int */ int } + _ interface{~int|~ /* ERROR overlapping terms ~int */ int } + _ interface{~int|MyInt /* ERROR overlapping terms p.MyInt and ~int */ } + _ interface{int|any} + _ interface{int|~string|union} + _ interface{int|~string|interface{int}} + _ interface{union|int} // interfaces (here: union) are ignored when checking for overlap + _ interface{union|union} // ditto + + // For now we do not permit interfaces with methods in unions. + _ interface{~ /* ERROR invalid use of ~ */ any} + _ interface{int|interface /* ERROR cannot use .* in union */ { m() }} +) + +type ( + // Tilde is not permitted on defined types or interfaces. + foo int + bar any + _ interface{foo} + _ interface{~ /* ERROR invalid use of ~ */ foo } + _ interface{~ /* ERROR invalid use of ~ */ bar } +) + +// Stand-alone type parameters are not permitted as elements or terms in unions. +type ( + _[T interface{ *T } ] struct{} // ok + _[T interface{ int | *T } ] struct{} // ok + _[T interface{ T /* ERROR term cannot be a type parameter */ } ] struct{} + _[T interface{ ~T /* ERROR type in term ~T cannot be a type parameter */ } ] struct{} + _[T interface{ int|T /* ERROR term cannot be a type parameter */ }] struct{} +) + +// Multiple embedded union elements are intersected. The order in which they +// appear in the interface doesn't matter since intersection is a symmetric +// operation. + +type myInt1 int +type myInt2 int + +func _[T interface{ myInt1|myInt2; ~int }]() T { return T(0) } +func _[T interface{ ~int; myInt1|myInt2 }]() T { return T(0) } + +// Here the intersections are empty - there's no type that's in the type set of T. +func _[T interface{ myInt1|myInt2; int }]() T { return T(0 /* ERROR cannot convert */ ) } +func _[T interface{ int; myInt1|myInt2 }]() T { return T(0 /* ERROR cannot convert */ ) } + +// Union elements may be interfaces as long as they don't define +// any methods or embed comparable. + +type ( + Integer interface{ ~int|~int8|~int16|~int32|~int64 } + Unsigned interface{ ~uint|~uint8|~uint16|~uint32|~uint64 } + Floats interface{ ~float32|~float64 } + Complex interface{ ~complex64|~complex128 } + Number interface{ Integer|Unsigned|Floats|Complex } + Ordered interface{ Integer|Unsigned|Floats|~string } + + _ interface{ Number | error /* ERROR cannot use error in union */ } + _ interface{ Ordered | comparable /* ERROR cannot use comparable in union */ } +) |