mirror of
https://github.com/golang/go
synced 2024-09-04 23:44:16 +00:00
![Robert Griesemer](/assets/img/avatar_default.png)
We can type-check these fine but the API implications are unclear. Fixes #50912. For #50937. Change-Id: If29bbb4a257ff6a85e3bfcd4755fd8f90c80fb87 Reviewed-on: https://go-review.googlesource.com/c/go/+/382116 Trust: Robert Griesemer <gri@golang.org> Run-TryBot: Robert Griesemer <gri@golang.org> Reviewed-by: Robert Findley <rfindley@google.com> TryBot-Result: Gopher Robot <gobot@golang.org>
122 lines
3.3 KiB
Go
122 lines
3.3 KiB
Go
// run -gcflags=-G=3
|
|
|
|
// Copyright 2022 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.
|
|
|
|
// absdiff example in which an Abs method is attached to a generic type, which is a
|
|
// structure with a single field that may be a list of possible basic types.
|
|
|
|
package main
|
|
|
|
import (
|
|
"fmt"
|
|
"math"
|
|
)
|
|
|
|
type Numeric interface {
|
|
~int | ~int8 | ~int16 | ~int32 | ~int64 |
|
|
~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
|
|
~float32 | ~float64 |
|
|
~complex64 | ~complex128
|
|
}
|
|
|
|
// numericAbs matches a struct containing a numeric type that has an Abs method.
|
|
type numericAbs[T Numeric] interface {
|
|
~struct{ Value T }
|
|
Abs() T
|
|
}
|
|
|
|
// absDifference computes the absolute value of the difference of
|
|
// a and b, where the absolute value is determined by the Abs method.
|
|
func absDifference[T Numeric, U numericAbs[T]](a, b U) T {
|
|
d := a.Value - b.Value
|
|
dt := U{Value: d}
|
|
return dt.Abs()
|
|
}
|
|
|
|
// orderedNumeric matches numeric types that support the < operator.
|
|
type orderedNumeric interface {
|
|
~int | ~int8 | ~int16 | ~int32 | ~int64 |
|
|
~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
|
|
~float32 | ~float64
|
|
}
|
|
|
|
// Complex matches the two complex types, which do not have a < operator.
|
|
type Complex interface {
|
|
~complex64 | ~complex128
|
|
}
|
|
|
|
// orderedAbs is a helper type that defines an Abs method for
|
|
// a struct containing an ordered numeric type.
|
|
type orderedAbs[T orderedNumeric] struct {
|
|
Value T
|
|
}
|
|
|
|
func (a orderedAbs[T]) Abs() T {
|
|
if a.Value < 0 {
|
|
return -a.Value
|
|
}
|
|
return a.Value
|
|
}
|
|
|
|
// complexAbs is a helper type that defines an Abs method for
|
|
// a struct containing a complex type.
|
|
type complexAbs[T Complex] struct {
|
|
Value T
|
|
}
|
|
|
|
func realimag(x any) (re, im float64) {
|
|
switch z := x.(type) {
|
|
case complex64:
|
|
re = float64(real(z))
|
|
im = float64(imag(z))
|
|
case complex128:
|
|
re = real(z)
|
|
im = imag(z)
|
|
default:
|
|
panic("unknown complex type")
|
|
}
|
|
return
|
|
}
|
|
|
|
func (a complexAbs[T]) Abs() T {
|
|
// TODO use direct conversion instead of realimag once #50937 is fixed
|
|
r, i := realimag(a.Value)
|
|
// r := float64(real(a.Value))
|
|
// i := float64(imag(a.Value))
|
|
d := math.Sqrt(r*r + i*i)
|
|
return T(complex(d, 0))
|
|
}
|
|
|
|
// OrderedAbsDifference returns the absolute value of the difference
|
|
// between a and b, where a and b are of an ordered type.
|
|
func OrderedAbsDifference[T orderedNumeric](a, b T) T {
|
|
return absDifference(orderedAbs[T]{a}, orderedAbs[T]{b})
|
|
}
|
|
|
|
// ComplexAbsDifference returns the absolute value of the difference
|
|
// between a and b, where a and b are of a complex type.
|
|
func ComplexAbsDifference[T Complex](a, b T) T {
|
|
return absDifference(complexAbs[T]{a}, complexAbs[T]{b})
|
|
}
|
|
|
|
func main() {
|
|
if got, want := OrderedAbsDifference(1.0, -2.0), 3.0; got != want {
|
|
panic(fmt.Sprintf("got = %v, want = %v", got, want))
|
|
}
|
|
if got, want := OrderedAbsDifference(-1.0, 2.0), 3.0; got != want {
|
|
panic(fmt.Sprintf("got = %v, want = %v", got, want))
|
|
}
|
|
if got, want := OrderedAbsDifference(-20, 15), 35; got != want {
|
|
panic(fmt.Sprintf("got = %v, want = %v", got, want))
|
|
}
|
|
|
|
if got, want := ComplexAbsDifference(5.0+2.0i, 2.0-2.0i), 5+0i; got != want {
|
|
panic(fmt.Sprintf("got = %v, want = %v", got, want))
|
|
}
|
|
if got, want := ComplexAbsDifference(2.0-2.0i, 5.0+2.0i), 5+0i; got != want {
|
|
panic(fmt.Sprintf("got = %v, want = %v", got, want))
|
|
}
|
|
}
|