1// run
2
3// Copyright 2020 The Go Authors. All rights reserved.
4// Use of this source code is governed by a BSD-style
5// license that can be found in the LICENSE file.
6
7package main
8
9type Numeric interface {
10	~int | ~int8 | ~int16 | ~int32 | ~int64 |
11		~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
12		~float32 | ~float64 |
13		~complex64 | ~complex128
14}
15
16// numericAbs matches numeric types with an Abs method.
17type numericAbs[T any] interface {
18	Numeric
19	Abs() T
20}
21
22// AbsDifference computes the absolute value of the difference of
23// a and b, where the absolute value is determined by the Abs method.
24func absDifference[T numericAbs[T]](a, b T) T {
25	d := a - b
26	return d.Abs()
27}
28
29// orderedNumeric matches numeric types that support the < operator.
30type orderedNumeric interface {
31	~int | ~int8 | ~int16 | ~int32 | ~int64 |
32		~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
33		~float32 | ~float64
34}
35
36// Complex matches the two complex types, which do not have a < operator.
37type Complex interface {
38	~complex64 | ~complex128
39}
40
41// For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
42// // orderedAbs is a helper type that defines an Abs method for
43// // ordered numeric types.
44// type orderedAbs[T orderedNumeric] T
45//
46// func (a orderedAbs[T]) Abs() orderedAbs[T] {
47// 	if a < 0 {
48// 		return -a
49// 	}
50// 	return a
51// }
52//
53// // complexAbs is a helper type that defines an Abs method for
54// // complex types.
55// type complexAbs[T Complex] T
56//
57// func (a complexAbs[T]) Abs() complexAbs[T] {
58// 	r := float64(real(a))
59// 	i := float64(imag(a))
60// 	d := math.Sqrt(r*r + i*i)
61// 	return complexAbs[T](complex(d, 0))
62// }
63//
64// // OrderedAbsDifference returns the absolute value of the difference
65// // between a and b, where a and b are of an ordered type.
66// func orderedAbsDifference[T orderedNumeric](a, b T) T {
67// 	return T(absDifference(orderedAbs[T](a), orderedAbs[T](b)))
68// }
69//
70// // ComplexAbsDifference returns the absolute value of the difference
71// // between a and b, where a and b are of a complex type.
72// func complexAbsDifference[T Complex](a, b T) T {
73// 	return T(absDifference(complexAbs[T](a), complexAbs[T](b)))
74// }
75
76func main() {
77	// // For now, a lone type parameter is not permitted as RHS in a type declaration (issue #45639).
78	// if got, want := orderedAbsDifference(1.0, -2.0), 3.0; got != want {
79	// 	panic(fmt.Sprintf("got = %v, want = %v", got, want))
80	// }
81	// if got, want := orderedAbsDifference(-1.0, 2.0), 3.0; got != want {
82	// 	panic(fmt.Sprintf("got = %v, want = %v", got, want))
83	// }
84	// if got, want := orderedAbsDifference(-20, 15), 35; got != want {
85	// 	panic(fmt.Sprintf("got = %v, want = %v", got, want))
86	// }
87	//
88	// if got, want := complexAbsDifference(5.0+2.0i, 2.0-2.0i), 5+0i; got != want {
89	// 	panic(fmt.Sprintf("got = %v, want = %v", got, want))
90	// }
91	// if got, want := complexAbsDifference(2.0-2.0i, 5.0+2.0i), 5+0i; got != want {
92	// 	panic(fmt.Sprintf("got = %v, want = %v", got, want))
93	// }
94}
95