# Source file test/typeparam/absdiff3.go

```     1  // run
2
4  // Use of this source code is governed by a BSD-style
6
7  // absdiff example using a function argument rather than attaching an
8  // Abs method to a structure containing base types.
9
10  package main
11
12  import (
13  	"fmt"
14  	"math"
15  )
16
17  type Numeric interface {
18  	OrderedNumeric | Complex
19  }
20
21  // absDifference computes the absolute value of the difference of
22  // a and b, where the absolute value is determined by the abs function.
23  func absDifference[T Numeric](a, b T, abs func(a T) T) T {
24  	return abs(a - b)
25  }
26
27  // OrderedNumeric matches numeric types that support the < operator.
28  type OrderedNumeric interface {
29  	~int | ~int8 | ~int16 | ~int32 | ~int64 |
30  		~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
31  		~float32 | ~float64
32  }
33
34  func Abs[T OrderedNumeric](a T) T {
35  	if a < 0 {
36  		return -a
37  	}
38  	return a
39  }
40
41  // Complex matches the two complex types, which do not have a < operator.
42  type Complex interface {
43  	~complex64 | ~complex128
44  }
45
46  func realimag(x any) (re, im float64) {
47  	switch z := x.(type) {
48  	case complex64:
49  		re = float64(real(z))
50  		im = float64(imag(z))
51  	case complex128:
52  		re = real(z)
53  		im = imag(z)
54  	default:
55  		panic("unknown complex type")
56  	}
57  	return
58  }
59
60  func ComplexAbs[T Complex](a T) T {
61  	// TODO use direct conversion instead of realimag once #50937 is fixed
62  	r, i := realimag(a)
63  	// r := float64(real(a))
64  	// i := float64(imag(a))
65  	d := math.Sqrt(r*r + i*i)
66  	return T(complex(d, 0))
67  }
68
69  // OrderedAbsDifference returns the absolute value of the difference
70  // between a and b, where a and b are of an ordered type.
71  func OrderedAbsDifference[T OrderedNumeric](a, b T) T {
72  	return absDifference(a, b, Abs[T])
73  }
74
75  // ComplexAbsDifference returns the absolute value of the difference
76  // between a and b, where a and b are of a complex type.
77  func ComplexAbsDifference[T Complex](a, b T) T {
78  	return absDifference(a, b, ComplexAbs[T])
79  }
80
81  func main() {
82  	if got, want := OrderedAbsDifference(1.0, -2.0), 3.0; got != want {
83  		panic(fmt.Sprintf("got = %v, want = %v", got, want))
84  	}
85  	if got, want := OrderedAbsDifference(-1.0, 2.0), 3.0; got != want {
86  		panic(fmt.Sprintf("got = %v, want = %v", got, want))
87  	}
88  	if got, want := OrderedAbsDifference(-20, 15), 35; got != want {
89  		panic(fmt.Sprintf("got = %v, want = %v", got, want))
90  	}
91
92  	if got, want := ComplexAbsDifference(5.0+2.0i, 2.0-2.0i), 5+0i; got != want {
93  		panic(fmt.Sprintf("got = %v, want = %v", got, want))
94  	}
95  	if got, want := ComplexAbsDifference(2.0-2.0i, 5.0+2.0i), 5+0i; got != want {
96  		panic(fmt.Sprintf("got = %v, want = %v", got, want))
97  	}
98  }
99
```

View as plain text