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// run
// Copyright 2021 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.
// Package slices provides functions for basic operations on
// slices of any element type.
package main
import (
"fmt"
"math"
"strings"
)
type Ordered interface {
~int | ~int8 | ~int16 | ~int32 | ~int64 |
~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr |
~float32 | ~float64 |
~string
}
type Integer interface {
~int | ~int8 | ~int16 | ~int32 | ~int64 |
~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr
}
// Max returns the maximum of two values of some ordered type.
func _Max[T Ordered](a, b T) T {
if a > b {
return a
}
return b
}
// Min returns the minimum of two values of some ordered type.
func _Min[T Ordered](a, b T) T {
if a < b {
return a
}
return b
}
// _Equal reports whether two slices are equal: the same length and all
// elements equal. All floating point NaNs are considered equal.
func _Equal[Elem comparable](s1, s2 []Elem) bool {
if len(s1) != len(s2) {
return false
}
for i, v1 := range s1 {
v2 := s2[i]
if v1 != v2 {
isNaN := func(f Elem) bool { return f != f }
if !isNaN(v1) || !isNaN(v2) {
return false
}
}
}
return true
}
// _EqualFn reports whether two slices are equal using a comparison
// function on each element.
func _EqualFn[Elem any](s1, s2 []Elem, eq func(Elem, Elem) bool) bool {
if len(s1) != len(s2) {
return false
}
for i, v1 := range s1 {
v2 := s2[i]
if !eq(v1, v2) {
return false
}
}
return true
}
// _Map turns a []Elem1 to a []Elem2 using a mapping function.
func _Map[Elem1, Elem2 any](s []Elem1, f func(Elem1) Elem2) []Elem2 {
r := make([]Elem2, len(s))
for i, v := range s {
r[i] = f(v)
}
return r
}
// _Reduce reduces a []Elem1 to a single value of type Elem2 using
// a reduction function.
func _Reduce[Elem1, Elem2 any](s []Elem1, initializer Elem2, f func(Elem2, Elem1) Elem2) Elem2 {
r := initializer
for _, v := range s {
r = f(r, v)
}
return r
}
// _Filter filters values from a slice using a filter function.
func _Filter[Elem any](s []Elem, f func(Elem) bool) []Elem {
var r []Elem
for _, v := range s {
if f(v) {
r = append(r, v)
}
}
return r
}
// _Max returns the maximum element in a slice of some ordered type.
// If the slice is empty it returns the zero value of the element type.
func _SliceMax[Elem Ordered](s []Elem) Elem {
if len(s) == 0 {
var zero Elem
return zero
}
return _Reduce(s[1:], s[0], _Max[Elem])
}
// _Min returns the minimum element in a slice of some ordered type.
// If the slice is empty it returns the zero value of the element type.
func _SliceMin[Elem Ordered](s []Elem) Elem {
if len(s) == 0 {
var zero Elem
return zero
}
return _Reduce(s[1:], s[0], _Min[Elem])
}
// _Append adds values to the end of a slice, returning a new slice.
// This is like the predeclared append function; it's an example
// of how to write it using generics. We used to write code like
// this before append was added to the language, but we had to write
// a separate copy for each type.
func _Append[T any](s []T, t ...T) []T {
lens := len(s)
tot := lens + len(t)
if tot <= cap(s) {
s = s[:tot]
} else {
news := make([]T, tot, tot+tot/2)
_Copy(news, s)
s = news
}
_Copy(s[lens:tot], t)
return s
}
// _Copy copies values from t to s, stopping when either slice is full,
// returning the number of values copied. This is like the predeclared
// copy function; it's an example of how to write it using generics.
func _Copy[T any](s, t []T) int {
i := 0
for ; i < len(s) && i < len(t); i++ {
s[i] = t[i]
}
return i
}
func TestEqual() {
s1 := []int{1, 2, 3}
if !_Equal(s1, s1) {
panic(fmt.Sprintf("_Equal(%v, %v) = false, want true", s1, s1))
}
s2 := []int{1, 2, 3}
if !_Equal(s1, s2) {
panic(fmt.Sprintf("_Equal(%v, %v) = false, want true", s1, s2))
}
s2 = append(s2, 4)
if _Equal(s1, s2) {
panic(fmt.Sprintf("_Equal(%v, %v) = true, want false", s1, s2))
}
s3 := []float64{1, 2, math.NaN()}
if !_Equal(s3, s3) {
panic(fmt.Sprintf("_Equal(%v, %v) = false, want true", s3, s3))
}
if _Equal(s1, nil) {
panic(fmt.Sprintf("_Equal(%v, nil) = true, want false", s1))
}
if _Equal(nil, s1) {
panic(fmt.Sprintf("_Equal(nil, %v) = true, want false", s1))
}
if !_Equal(s1[:0], nil) {
panic(fmt.Sprintf("_Equal(%v, nil = false, want true", s1[:0]))
}
}
func offByOne[Elem Integer](a, b Elem) bool {
return a == b+1 || a == b-1
}
func TestEqualFn() {
s1 := []int{1, 2, 3}
s2 := []int{2, 3, 4}
if _EqualFn(s1, s1, offByOne[int]) {
panic(fmt.Sprintf("_EqualFn(%v, %v, offByOne) = true, want false", s1, s1))
}
if !_EqualFn(s1, s2, offByOne[int]) {
panic(fmt.Sprintf("_EqualFn(%v, %v, offByOne) = false, want true", s1, s2))
}
if !_EqualFn(s1[:0], nil, offByOne[int]) {
panic(fmt.Sprintf("_EqualFn(%v, nil, offByOne) = false, want true", s1[:0]))
}
s3 := []string{"a", "b", "c"}
s4 := []string{"A", "B", "C"}
if !_EqualFn(s3, s4, strings.EqualFold) {
panic(fmt.Sprintf("_EqualFn(%v, %v, strings.EqualFold) = false, want true", s3, s4))
}
}
func TestMap() {
s1 := []int{1, 2, 3}
s2 := _Map(s1, func(i int) float64 { return float64(i) * 2.5 })
if want := []float64{2.5, 5, 7.5}; !_Equal(s2, want) {
panic(fmt.Sprintf("_Map(%v, ...) = %v, want %v", s1, s2, want))
}
s3 := []string{"Hello", "World"}
s4 := _Map(s3, strings.ToLower)
if want := []string{"hello", "world"}; !_Equal(s4, want) {
panic(fmt.Sprintf("_Map(%v, strings.ToLower) = %v, want %v", s3, s4, want))
}
s5 := _Map(nil, func(i int) int { return i })
if len(s5) != 0 {
panic(fmt.Sprintf("_Map(nil, identity) = %v, want empty slice", s5))
}
}
func TestReduce() {
s1 := []int{1, 2, 3}
r := _Reduce(s1, 0, func(f float64, i int) float64 { return float64(i)*2.5 + f })
if want := 15.0; r != want {
panic(fmt.Sprintf("_Reduce(%v, 0, ...) = %v, want %v", s1, r, want))
}
if got := _Reduce(nil, 0, func(i, j int) int { return i + j }); got != 0 {
panic(fmt.Sprintf("_Reduce(nil, 0, add) = %v, want 0", got))
}
}
func TestFilter() {
s1 := []int{1, 2, 3}
s2 := _Filter(s1, func(i int) bool { return i%2 == 0 })
if want := []int{2}; !_Equal(s2, want) {
panic(fmt.Sprintf("_Filter(%v, even) = %v, want %v", s1, s2, want))
}
if s3 := _Filter(s1[:0], func(i int) bool { return true }); len(s3) > 0 {
panic(fmt.Sprintf("_Filter(%v, identity) = %v, want empty slice", s1[:0], s3))
}
}
func TestMax() {
s1 := []int{1, 2, 3, -5}
if got, want := _SliceMax(s1), 3; got != want {
panic(fmt.Sprintf("_Max(%v) = %d, want %d", s1, got, want))
}
s2 := []string{"aaa", "a", "aa", "aaaa"}
if got, want := _SliceMax(s2), "aaaa"; got != want {
panic(fmt.Sprintf("_Max(%v) = %q, want %q", s2, got, want))
}
if got, want := _SliceMax(s2[:0]), ""; got != want {
panic(fmt.Sprintf("_Max(%v) = %q, want %q", s2[:0], got, want))
}
}
func TestMin() {
s1 := []int{1, 2, 3, -5}
if got, want := _SliceMin(s1), -5; got != want {
panic(fmt.Sprintf("_Min(%v) = %d, want %d", s1, got, want))
}
s2 := []string{"aaa", "a", "aa", "aaaa"}
if got, want := _SliceMin(s2), "a"; got != want {
panic(fmt.Sprintf("_Min(%v) = %q, want %q", s2, got, want))
}
if got, want := _SliceMin(s2[:0]), ""; got != want {
panic(fmt.Sprintf("_Min(%v) = %q, want %q", s2[:0], got, want))
}
}
func TestAppend() {
s := []int{1, 2, 3}
s = _Append(s, 4, 5, 6)
want := []int{1, 2, 3, 4, 5, 6}
if !_Equal(s, want) {
panic(fmt.Sprintf("after _Append got %v, want %v", s, want))
}
}
func TestCopy() {
s1 := []int{1, 2, 3}
s2 := []int{4, 5}
if got := _Copy(s1, s2); got != 2 {
panic(fmt.Sprintf("_Copy returned %d, want 2", got))
}
want := []int{4, 5, 3}
if !_Equal(s1, want) {
panic(fmt.Sprintf("after _Copy got %v, want %v", s1, want))
}
}
func main() {
TestEqual()
TestEqualFn()
TestMap()
TestReduce()
TestFilter()
TestMax()
TestMin()
TestAppend()
TestCopy()
}