maps: new package

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

Fixes golang#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>

api/next/57436.txt

@@ -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

src/go/build/deps_test.go

@@ -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.

src/maps/maps.go

@@ -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)
+		}
+	}
+}

src/maps/maps_test.go

@@ -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)
+	}
+}