putIfAbsent method

V putIfAbsent (
  1. K key,
  2. V 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.

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

V putIfAbsent(K key, V ifAbsent());

© 2012 the Dart project authors
Licensed under the Creative Commons Attribution-ShareAlike License v4.0.
https://api.dart.dev/stable/2.13.0/dart-core/Map/putIfAbsent.html