putIfAbsent method Null safety
override
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
String putIfAbsent(String key, String ifAbsent()) {
if (!containsKey(key)) this[key] = ifAbsent();
return this[key] as String;
}