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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)) } }