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// Copyright 2023 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.
// The immutable package defines immutable wrappers around common data
// structures. These are used for additional type safety inside gopls.
// See the "persistent" package for copy-on-write data structures.
package immutable
// Map is an immutable wrapper around an ordinary Go map.
type Map[K comparable, V any] struct {
m map[K]V
// MapOf wraps the given Go map.
// The caller must not subsequently mutate the map.
func MapOf[K comparable, V any](m map[K]V) Map[K, V] {
return Map[K, V]{m}
// Keys returns all keys present in the map.
func (m Map[K, V]) Keys() []K {
var keys []K
for k := range m.m {
keys = append(keys, k)
return keys
// Value returns the mapped value for k.
// It is equivalent to the commaok form of an ordinary go map, and returns
// (zero, false) if the key is not present.
func (m Map[K, V]) Value(k K) (V, bool) {
v, ok := m.m[k]
return v, ok
// Len returns the number of entries in the Map.
func (m Map[K, V]) Len() int {
return len(m.m)
// Range calls f for each mapped (key, value) pair.
// There is no way to break out of the loop.
// TODO: generalize when Go iterators (#61405) land.
func (m Map[K, V]) Range(f func(k K, v V)) {
for k, v := range m.m {
f(k, v)