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maps: new package
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This copies x/exp/maps into the standard library (except for the Clear
function which is now available as the clear builtin.)

Fixes #57436

Change-Id: I30dd470c2f7ae34c7c82b4c1025a7582d61fabaa
Reviewed-on: https://go-review.googlesource.com/c/go/+/464343
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Eli Bendersky <eliben@google.com>
Run-TryBot: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
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ianlancetaylor authored and gopherbot committed Feb 3, 2023
1 parent 10643b7 commit a964876
Showing 5 changed files with 277 additions and 1 deletion.
7 changes: 7 additions & 0 deletions api/next/57436.txt
Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
pkg maps, func Clone[$0 interface{ ~map[$1]$2 }, $1 comparable, $2 interface{}]($0) $0 #57436
pkg maps, func Copy[$0 interface{ ~map[$2]$3 }, $1 interface{ ~map[$2]$3 }, $2 comparable, $3 interface{}]($0, $1) #57436
pkg maps, func DeleteFunc[$0 interface{ ~map[$1]$2 }, $1 comparable, $2 interface{}]($0, func($1, $2) bool) #57436
pkg maps, func EqualFunc[$0 interface{ ~map[$2]$3 }, $1 interface{ ~map[$2]$4 }, $2 comparable, $3 interface{}, $4 interface{}]($0, $1, func($3, $4) bool) bool #57436
pkg maps, func Equal[$0 interface{ ~map[$2]$3 }, $1 interface{ ~map[$2]$3 }, $2 comparable, $3 comparable]($0, $1) bool #57436
pkg maps, func Keys[$0 interface{ ~map[$1]$2 }, $1 comparable, $2 interface{}]($0) []$1 #57436
pkg maps, func Values[$0 interface{ ~map[$1]$2 }, $1 comparable, $2 interface{}]($0) []$2 #57436
2 changes: 1 addition & 1 deletion src/go/build/deps_test.go
Original file line number Diff line number Diff line change
@@ -45,7 +45,7 @@ var depsRules = `
internal/cpu, internal/goarch,
internal/goexperiment, internal/goos,
internal/goversion, internal/nettrace, internal/platform,
unicode/utf8, unicode/utf16, unicode,
maps, unicode/utf8, unicode/utf16, unicode,
unsafe;
# These packages depend only on internal/goarch and unsafe.
1 change: 1 addition & 0 deletions src/go/doc/comment/std.go

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87 changes: 87 additions & 0 deletions src/maps/maps.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,87 @@
// 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 maps defines various functions useful with maps of any type.
package maps

// Keys returns the keys of the map m.
// The keys will be in an indeterminate order.
func Keys[M ~map[K]V, K comparable, V any](m M) []K {
r := make([]K, 0, len(m))
for k := range m {
r = append(r, k)
}
return r
}

// Values returns the values of the map m.
// The values will be in an indeterminate order.
func Values[M ~map[K]V, K comparable, V any](m M) []V {
r := make([]V, 0, len(m))
for _, v := range m {
r = append(r, v)
}
return r
}

// Equal reports whether two maps contain the same key/value pairs.
// Values are compared using ==.
func Equal[M1, M2 ~map[K]V, K, V comparable](m1 M1, m2 M2) bool {
if len(m1) != len(m2) {
return false
}
for k, v1 := range m1 {
if v2, ok := m2[k]; !ok || v1 != v2 {
return false
}
}
return true
}

// EqualFunc is like Equal, but compares values using eq.
// Keys are still compared with ==.
func EqualFunc[M1 ~map[K]V1, M2 ~map[K]V2, K comparable, V1, V2 any](m1 M1, m2 M2, eq func(V1, V2) bool) bool {
if len(m1) != len(m2) {
return false
}
for k, v1 := range m1 {
if v2, ok := m2[k]; !ok || !eq(v1, v2) {
return false
}
}
return true
}

// Clone returns a copy of m. This is a shallow clone:
// the new keys and values are set using ordinary assignment.
func Clone[M ~map[K]V, K comparable, V any](m M) M {
// Preserve nil in case it matters.
if m == nil {
return nil
}
r := make(M, len(m))
for k, v := range m {
r[k] = v
}
return r
}

// Copy copies all key/value pairs in src adding them to dst.
// When a key in src is already present in dst,
// the value in dst will be overwritten by the value associated
// with the key in src.
func Copy[M1 ~map[K]V, M2 ~map[K]V, K comparable, V any](dst M1, src M2) {
for k, v := range src {
dst[k] = v
}
}

// DeleteFunc deletes any key/value pairs from m for which del returns true.
func DeleteFunc[M ~map[K]V, K comparable, V any](m M, del func(K, V) bool) {
for k, v := range m {
if del(k, v) {
delete(m, k)
}
}
}
181 changes: 181 additions & 0 deletions src/maps/maps_test.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,181 @@
// 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 maps

import (
"math"
"sort"
"strconv"
"testing"
)

// TODO: replace with slices.Equal when slices is in GOROOT.
func slicesEqual[E comparable](s1, s2 []E) bool {
if len(s1) != len(s2) {
return false
}
for i := range s1 {
if s1[i] != s2[i] {
return false
}
}
return true
}

var m1 = map[int]int{1: 2, 2: 4, 4: 8, 8: 16}
var m2 = map[int]string{1: "2", 2: "4", 4: "8", 8: "16"}

func TestKeys(t *testing.T) {
want := []int{1, 2, 4, 8}

got1 := Keys(m1)
sort.Ints(got1)
if !slicesEqual(got1, want) {
t.Errorf("Keys(%v) = %v, want %v", m1, got1, want)
}

got2 := Keys(m2)
sort.Ints(got2)
if !slicesEqual(got2, want) {
t.Errorf("Keys(%v) = %v, want %v", m2, got2, want)
}
}

func TestValues(t *testing.T) {
got1 := Values(m1)
want1 := []int{2, 4, 8, 16}
sort.Ints(got1)
if !slicesEqual(got1, want1) {
t.Errorf("Values(%v) = %v, want %v", m1, got1, want1)
}

got2 := Values(m2)
want2 := []string{"16", "2", "4", "8"}
sort.Strings(got2)
if !slicesEqual(got2, want2) {
t.Errorf("Values(%v) = %v, want %v", m2, got2, want2)
}
}

func TestEqual(t *testing.T) {
if !Equal(m1, m1) {
t.Errorf("Equal(%v, %v) = false, want true", m1, m1)
}
if Equal(m1, (map[int]int)(nil)) {
t.Errorf("Equal(%v, nil) = true, want false", m1)
}
if Equal((map[int]int)(nil), m1) {
t.Errorf("Equal(nil, %v) = true, want false", m1)
}
if !Equal[map[int]int, map[int]int](nil, nil) {
t.Error("Equal(nil, nil) = false, want true")
}
if ms := map[int]int{1: 2}; Equal(m1, ms) {
t.Errorf("Equal(%v, %v) = true, want false", m1, ms)
}

// Comparing NaN for equality is expected to fail.
mf := map[int]float64{1: 0, 2: math.NaN()}
if Equal(mf, mf) {
t.Errorf("Equal(%v, %v) = true, want false", mf, mf)
}
}

// equal is simply ==.
func equal[T comparable](v1, v2 T) bool {
return v1 == v2
}

// equalNaN is like == except that all NaNs are equal.
func equalNaN[T comparable](v1, v2 T) bool {
isNaN := func(f T) bool { return f != f }
return v1 == v2 || (isNaN(v1) && isNaN(v2))
}

// equalStr compares ints and strings.
func equalIntStr(v1 int, v2 string) bool {
return strconv.Itoa(v1) == v2
}

func TestEqualFunc(t *testing.T) {
if !EqualFunc(m1, m1, equal[int]) {
t.Errorf("EqualFunc(%v, %v, equal) = false, want true", m1, m1)
}
if EqualFunc(m1, (map[int]int)(nil), equal[int]) {
t.Errorf("EqualFunc(%v, nil, equal) = true, want false", m1)
}
if EqualFunc((map[int]int)(nil), m1, equal[int]) {
t.Errorf("EqualFunc(nil, %v, equal) = true, want false", m1)
}
if !EqualFunc[map[int]int, map[int]int](nil, nil, equal[int]) {
t.Error("EqualFunc(nil, nil, equal) = false, want true")
}
if ms := map[int]int{1: 2}; EqualFunc(m1, ms, equal[int]) {
t.Errorf("EqualFunc(%v, %v, equal) = true, want false", m1, ms)
}

// Comparing NaN for equality is expected to fail.
mf := map[int]float64{1: 0, 2: math.NaN()}
if EqualFunc(mf, mf, equal[float64]) {
t.Errorf("EqualFunc(%v, %v, equal) = true, want false", mf, mf)
}
// But it should succeed using equalNaN.
if !EqualFunc(mf, mf, equalNaN[float64]) {
t.Errorf("EqualFunc(%v, %v, equalNaN) = false, want true", mf, mf)
}

if !EqualFunc(m1, m2, equalIntStr) {
t.Errorf("EqualFunc(%v, %v, equalIntStr) = false, want true", m1, m2)
}
}

func TestClone(t *testing.T) {
mc := Clone(m1)
if !Equal(mc, m1) {
t.Errorf("Clone(%v) = %v, want %v", m1, mc, m1)
}
mc[16] = 32
if Equal(mc, m1) {
t.Errorf("Equal(%v, %v) = true, want false", mc, m1)
}
}

func TestCloneNil(t *testing.T) {
var m1 map[string]int
mc := Clone(m1)
if mc != nil {
t.Errorf("Clone(%v) = %v, want %v", m1, mc, m1)
}
}

func TestCopy(t *testing.T) {
mc := Clone(m1)
Copy(mc, mc)
if !Equal(mc, m1) {
t.Errorf("Copy(%v, %v) = %v, want %v", m1, m1, mc, m1)
}
Copy(mc, map[int]int{16: 32})
want := map[int]int{1: 2, 2: 4, 4: 8, 8: 16, 16: 32}
if !Equal(mc, want) {
t.Errorf("Copy result = %v, want %v", mc, want)
}

type M1 map[int]bool
type M2 map[int]bool
Copy(make(M1), make(M2))
}

func TestDeleteFunc(t *testing.T) {
mc := Clone(m1)
DeleteFunc(mc, func(int, int) bool { return false })
if !Equal(mc, m1) {
t.Errorf("DeleteFunc(%v, true) = %v, want %v", m1, mc, m1)
}
DeleteFunc(mc, func(k, v int) bool { return k > 3 })
want := map[int]int{1: 2, 2: 4}
if !Equal(mc, want) {
t.Errorf("DeleteFunc result = %v, want %v", mc, want)
}
}

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