diff options
Diffstat (limited to 'test/typeparam/absdiff2.go')
-rw-r--r-- | test/typeparam/absdiff2.go | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/test/typeparam/absdiff2.go b/test/typeparam/absdiff2.go new file mode 100644 index 0000000..87a1ec6 --- /dev/null +++ b/test/typeparam/absdiff2.go @@ -0,0 +1,135 @@ +// 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)) + } +} |