operator []= method
Implementation
void operator []=(K key, V value) {
if (key == null) throw new ArgumentError(key);
// Splay on the key to move the last node on the search path for
// the key to the root of the tree.
int comp = _splay(key);
if (comp == 0) {
_root.value = value;
return;
}
_addNewRoot(new _SplayTreeMapNode(key, value), comp);
}