putIfAbsent method

  1. @override
V putIfAbsent (
  1. K key,
  2. V ifAbsent(
      )
    )
    override

    Look up the value of key, or add a new value 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.

    Map<String, int> scores = {'Bob': 36};
    for (var key in ['Bob', 'Rohan', 'Sophena']) {
      scores.putIfAbsent(key, () => key.length);
    }
    scores['Bob'];      // 36
    scores['Rohan'];    //  5
    scores['Sophena'];  //  7
    

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

    Implementation

    @override
    V putIfAbsent(K key, V ifAbsent()) {
      _items.forEach((entry){
        print(entry);
      });
      return null;
    }