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// 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 (
// Type lists are processed as unions but an error is reported.
// TODO(gri) remove this once the parser doesn't accept type lists anymore.
_ interface{
type /* ERROR use generalized embedding syntax instead of a type list */ int
}
_ interface{
type /* ERROR use generalized embedding syntax instead of a type list */ int
type float32
}
)
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|interface{}}
_ interface{int|~string|union}
_ interface{int|~string|interface{int}}
_ interface{union|union /* ERROR overlapping terms p.union and p.union */ }
// For now we do not permit interfaces with methods in unions.
_ interface{~ /* ERROR invalid use of ~ */ interface{}}
_ interface{int|interface /* ERROR cannot use .* in union */ { m() }}
)
type (
// Tilde is not permitted on defined types or interfaces.
foo int
bar interface{}
_ 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 cannot embed a type parameter */ } ] struct{}
_[T interface{ ~T /* ERROR cannot embed a type parameter */ } ] struct{}
_[T interface{ int|T /* ERROR cannot embed 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 */ }
)
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