put method

void put(K key, V value)

Associates value with key, replacing any previous value. Cancels the previous finalization and attaches a new one. When the key is GC-collected, onFinalize is called with the value.

Implementation

void put(K key, V value) {
  final prevBox = _expando[key];
  if (prevBox != null) {
    if (identical(prevBox.value, value)) {
      // Same object already associated → avoid detach/attach churn.
      return;
    }

    // Cancel pending finalization for the previous value because the
    // association is being replaced.
    _finalizer.detach(prevBox);
  }

  final box = _ExpandoBox<V>(value);

  // Weakly associate value with the key.
  _expando[key] = box;

  // Attach finalization to the key lifecycle.
  // When key is GC-collected, `_onFinalize(box)` will be invoked.
  // `detach: box` allows later manual cancellation via detach(box).
  _finalizer.attach(key, box, detach: box);
}