maps: new package
For golang/go#47649
Change-Id: I49c9b1aab0e2204bde7b7e21d68130551118bf92
Reviewed-on: https://go-review.googlesource.com/c/exp/+/364875
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
diff --git a/maps/maps.go b/maps/maps.go
new file mode 100644
index 0000000..9bed0bf
--- /dev/null
+++ b/maps/maps.go
@@ -0,0 +1,90 @@
+// 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
+}
+
+// Clear removes all entries from m, leaving it empty.
+func Clear[M ~map[K]V, K comparable, V any](m M) {
+ for k := range m {
+ delete(m, k)
+ }
+}
+
+// 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 {
+ 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[M map[K]V, K comparable, V any](dst, src M) {
+ 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)
+ }
+ }
+}
diff --git a/maps/maps_test.go b/maps/maps_test.go
new file mode 100644
index 0000000..8be7f74
--- /dev/null
+++ b/maps/maps_test.go
@@ -0,0 +1,169 @@
+// 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"
+
+ "golang.org/x/exp/slices"
+)
+
+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 !slices.Equal(got1, want) {
+ t.Errorf("Keys(%v) = %v, want %v", m1, got1, want)
+ }
+
+ got2 := Keys(m2)
+ sort.Ints(got2)
+ if !slices.Equal(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 !slices.Equal(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 !slices.Equal(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, nil) {
+ t.Errorf("Equal(%v, nil) = true, want false", m1)
+ }
+ if Equal(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, nil, equal[int]) {
+ t.Errorf("EqualFunc(%v, nil, equal) = true, want false", m1)
+ }
+ if EqualFunc(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 TestClear(t *testing.T) {
+ ml := map[int]int{1: 1, 2: 2, 3: 3}
+ Clear(ml)
+ if got := len(ml); got != 0 {
+ t.Errorf("len(%v) = %d after Clear, want 0", ml, got)
+ }
+ if !Equal(ml, nil) {
+ t.Errorf("Equal(%v, nil) = false, want true", ml)
+ }
+}
+
+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 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)
+ }
+}
+
+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)
+ }
+}
