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// run
// 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
Value() 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_
}
// Field accesses through type parameters are disabled
// until we have a more thorough understanding of the
// implications on the spec. See issue #51576.
// Use accessor method instead.
func (a orderedAbs[T]) Value() T {
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))
}
func (a complexAbs[T]) Value() T {
return a.Value_
}
// 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))
}
}