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// run -gcflags=-G=3
// Copyright 2020 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.
package main
import (
"fmt"
"math"
)
type Numeric interface {
type int, int8, int16, int32, int64,
uint, uint8, uint16, uint32, uint64, uintptr,
float32, float64,
complex64, complex128
}
// numericAbs matches numeric types with an Abs method.
type numericAbs[T any] interface {
Numeric
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 numericAbs[T]](a, b T) T {
d := a - b
return d.Abs()
}
// orderedNumeric matches numeric types that support the < operator.
type orderedNumeric interface {
type 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 {
type complex64, complex128
}
// orderedAbs is a helper type that defines an Abs method for
// ordered numeric types.
type orderedAbs[T orderedNumeric] T
func (a orderedAbs[T]) Abs() orderedAbs[T] {
// TODO(danscales): orderedAbs[T] conversion shouldn't be needed
if a < orderedAbs[T](0) {
return -a
}
return a
}
// complexAbs is a helper type that defines an Abs method for
// complex types.
type complexAbs[T Complex] T
func (a complexAbs[T]) Abs() complexAbs[T] {
r := float64(real(a))
i := float64(imag(a))
d := math.Sqrt(r * r + i * i)
return complexAbs[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 T(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 T(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))
}
}
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