putIfAbsent method

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;
}