putIfAbsent method

dynamic putIfAbsent(
  1. String key,
  2. dynamic ifAbsent(

    Look up the value of key, or add a new entry if it isn't there.

    Returns the value associated to key, if there is one. Otherwise calls ifAbsent to get a new value, associates key to that value, and then returns the new value.

    final diameters = <num, String>{1.0: 'Earth'};
    final otherDiameters = <double, String>{0.383: 'Mercury', 0.949: 'Venus'};
    for (final item in otherDiameters.entries) {
      diameters.putIfAbsent(item.key, () => item.value);
    print(diameters); // {1.0: Earth, 0.383: Mercury, 0.949: Venus}
    // If the key already exists, the current value is returned.
    final result = diameters.putIfAbsent(0.383, () => 'Random');
    print(result); // Mercury
    print(diameters); // {1.0: Earth, 0.383: Mercury, 0.949: Venus}

    Calling ifAbsent must not add or remove keys from the map.


    dynamic putIfAbsent(String key, dynamic ifAbsent()) {
      throw new UnsupportedError("Not supported");