golang constraints 代码
文件路径：/src/go/types/testdata/examples/constraints.go
/ 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 */ }
)