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a91d0b649c
We may revisit this decision in a future release. By disallowing this for Go 1.18 we are ensuring that we don't lock in the generics design in a place that may need to change later. (Type declarations are the primary construct where it crucially matters what the underlying type of a type parameter is.) Comment out all tests that rely on this feature; add comments referring to issue so we can find all places easily should we change our minds. Fixes #45639. Change-Id: I730510e4da66d3716d455a9071c7778a1e4a1152 Reviewed-on: https://go-review.googlesource.com/c/go/+/359177 Trust: Robert Griesemer <gri@golang.org> Trust: Dan Scales <danscales@google.com> Reviewed-by: Dan Scales <danscales@google.com>
95 lines
3 KiB
Go
95 lines
3 KiB
Go
// run -gcflags=-G=3
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// Copyright 2020 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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type Numeric interface {
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~int | ~int8 | ~int16 | ~int32 | ~int64 |
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~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
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~float32 | ~float64 |
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~complex64 | ~complex128
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}
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// numericAbs matches numeric types with an Abs method.
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type numericAbs[T any] interface {
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Numeric
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Abs() T
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}
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// AbsDifference computes the absolute value of the difference of
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// a and b, where the absolute value is determined by the Abs method.
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func absDifference[T numericAbs[T]](a, b T) T {
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d := a - b
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return d.Abs()
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}
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// orderedNumeric matches numeric types that support the < operator.
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type orderedNumeric interface {
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~int | ~int8 | ~int16 | ~int32 | ~int64 |
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~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
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~float32 | ~float64
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}
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// Complex matches the two complex types, which do not have a < operator.
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type Complex interface {
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~complex64 | ~complex128
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}
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// For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
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// // orderedAbs is a helper type that defines an Abs method for
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// // ordered numeric types.
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// type orderedAbs[T orderedNumeric] T
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//
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// func (a orderedAbs[T]) Abs() orderedAbs[T] {
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// if a < 0 {
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// return -a
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// }
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// return a
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// }
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//
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// // complexAbs is a helper type that defines an Abs method for
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// // complex types.
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// type complexAbs[T Complex] T
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//
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// func (a complexAbs[T]) Abs() complexAbs[T] {
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// r := float64(real(a))
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// i := float64(imag(a))
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// d := math.Sqrt(r*r + i*i)
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// return complexAbs[T](complex(d, 0))
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// }
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//
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// // OrderedAbsDifference returns the absolute value of the difference
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// // between a and b, where a and b are of an ordered type.
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// func orderedAbsDifference[T orderedNumeric](a, b T) T {
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// return T(absDifference(orderedAbs[T](a), orderedAbs[T](b)))
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// }
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//
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// // ComplexAbsDifference returns the absolute value of the difference
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// // between a and b, where a and b are of a complex type.
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// func complexAbsDifference[T Complex](a, b T) T {
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// return T(absDifference(complexAbs[T](a), complexAbs[T](b)))
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// }
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func main() {
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// // For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
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// if got, want := orderedAbsDifference(1.0, -2.0), 3.0; got != want {
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// panic(fmt.Sprintf("got = %v, want = %v", got, want))
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// }
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// if got, want := orderedAbsDifference(-1.0, 2.0), 3.0; got != want {
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// panic(fmt.Sprintf("got = %v, want = %v", got, want))
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// }
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// if got, want := orderedAbsDifference(-20, 15), 35; got != want {
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// panic(fmt.Sprintf("got = %v, want = %v", got, want))
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// }
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//
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// if got, want := complexAbsDifference(5.0+2.0i, 2.0-2.0i), 5+0i; got != want {
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// panic(fmt.Sprintf("got = %v, want = %v", got, want))
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// }
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// if got, want := complexAbsDifference(2.0-2.0i, 5.0+2.0i), 5+0i; got != want {
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// panic(fmt.Sprintf("got = %v, want = %v", got, want))
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// }
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}
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