1 files changed, 98 insertions, 0 deletions
diff --git a/test/typeparam/absdiff3.go b/test/typeparam/absdiff3.go
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+++ b/test/typeparam/absdiff3.go
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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 using a function argument rather than attaching an
+// Abs method to a structure containing base types.
+
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+type Numeric interface {
+	OrderedNumeric | Complex
+}
+
+// absDifference computes the absolute value of the difference of
+// a and b, where the absolute value is determined by the abs function.
+func absDifference[T Numeric](a, b T, abs func(a T) T) T {
+	return abs(a - b)
+}
+
+// OrderedNumeric matches numeric types that support the < operator.
+type OrderedNumeric interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64 |
+		~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
+		~float32 | ~float64
+}
+
+func Abs[T OrderedNumeric](a T) T {
+	if a < 0 {
+		return -a
+	}
+	return a
+}
+
+// Complex matches the two complex types, which do not have a < operator.
+type Complex interface {
+	~complex64 | ~complex128
+}
+
+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 ComplexAbs[T Complex](a T) T {
+	// TODO use direct conversion instead of realimag once #50937 is fixed
+	r, i := realimag(a)
+	// r := float64(real(a))
+	// i := float64(imag(a))
+	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(a, b, Abs[T])
+}
+
+// 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(a, b, ComplexAbs[T])
+}
+
+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))
+	}
+}