putIfAbsent method

V putIfAbsent(K key, V ifAbsent())

This operation is not supported by an unmodifiable map.

Source

V putIfAbsent(K key, V ifAbsent()) {
  throw new UnsupportedError("Cannot modify unmodifiable map");
}

© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dartlang.org/stable/1.24.3/dart-collection/UnmodifiableMapView/putIfAbsent.html