# putIfAbsent method

V putIfAbsent (K key, V ifAbsent())

## Implementation

    V putIfAbsent(K key, V ifAbsent()) {
      if (key == null) throw new ArgumentError(key);
      int comp = _splay(key);
      if (comp == 0) {
        return _root.value;
      }
      int modificationCount = _modificationCount;
      int splayCount = _splayCount;
      V value = ifAbsent();
      if (modificationCount != _modificationCount) {
        throw new ConcurrentModificationError(this);
      }
      if (splayCount != _splayCount) {
        comp = _splay(key);
        // Key is still not there, otherwise _modificationCount would be changed.
        assert(comp != 0);
      }
      _addNewRoot(new _SplayTreeMapNode(key, value), comp);
      return value;
    }