Add immutability option

README.md

@@ -19,5 +19,5 @@ biMap.Size() // == 0
 biMap2 := bimap.NewBiMap()
 biMap2.Insert("key", 1) // Notice different types
 val, ok := biMap2.Get("key") // Returns 1
-val, ok = biMap2.InverseGet(1) //Return "key"
+val, ok = biMap2.InverseGet(1) // Returns "key"
 ```

bimap.go

@@ -4,16 +4,23 @@ import "sync"
 
 type biMap struct {
 	s sync.RWMutex
+	immutable bool
 	forward map[interface{}]interface{}
 	inverse map[interface{}]interface{}
 }
 
 func NewBiMap() *biMap {
-	return &biMap{forward: make(map[interface{}]interface{}), inverse: make(map[interface{}]interface{})}
+	return &biMap{forward: make(map[interface{}]interface{}), inverse: make(map[interface{}]interface{}), immutable:false}
 }
 
 
 func (b *biMap) Insert(k interface{}, v interface{}) {
+	b.s.RLock()
+	if b.immutable {
+		panic("Cannot modify immutable map")
+	}
+	b.s.RUnlock()
+
 	b.s.Lock()
 	defer b.s.Unlock()
 	b.forward[k] = v
@@ -56,6 +63,12 @@ func (b *biMap) InverseGet(v interface{}) (interface{}, bool) {
 }
 
 func (b *biMap) Delete(k interface{}) {
+	b.s.RLock()
+	if b.immutable {
+		panic("Cannot modify immutable map")
+	}
+	b.s.RUnlock()
+
 	if !b.Exists(k) {
 		return
 	}
@@ -67,6 +80,12 @@ func (b *biMap) Delete(k interface{}) {
 }
 
 func (b *biMap) InverseDelete(v interface{}) {
+	b.s.RLock()
+	if b.immutable {
+		panic("Cannot modify immutable map")
+	}
+	b.s.RUnlock()
+
 	if !b.InverseExists(v) {
 		return
 	}
@@ -83,4 +102,10 @@ func (b*biMap) Size() int{
 	b.s.RLock()
 	defer b.s.RUnlock()
 	return len(b.forward)
+}
+
+func (b *biMap) SetImmutable() {
+	b.s.Lock()
+	defer b.s.Unlock()
+	b.immutable = true
 }

bimap_test.go

@@ -154,6 +154,44 @@ func TestBiMap_WithVaryingType(t *testing.T) {
 
 }
 
+func TestBiMap_SetImmutable(t *testing.T) {
+	actual := NewBiMap()
+	dummyKey := "Dummy key"
+	dummyVal := 3
+
+	actual.Insert(dummyKey, dummyVal)
+
+	actual.SetImmutable()
+
+	assert.Panics(t, func() {
+		actual.Delete(dummyKey)
+	}, "It should panic on a mutation operation")
+
+	val, _ := actual.Get(dummyKey)
+
+	assert.Equal(t, dummyVal, val, "It should still have the value")
+
+	assert.Panics(t, func() {
+		actual.InverseDelete(dummyVal)
+	}, "It should panic on a mutation operation")
+
+	key, _ := actual.InverseGet(dummyVal)
+
+	assert.Equal(t, dummyKey, key, "It should still have the key")
+
+	size := actual.Size()
+
+	assert.Equal(t, 1, size, "Size should be one")
+
+	assert.Panics(t, func() {
+		actual.Insert("New", 1)
+	}, "It should panic on a mutation operation")
+
+	size = actual.Size()
+
+	assert.Equal(t, 1, size, "Size should be one")
+
+}