Set

A set in Dart is an unordered collection of unique items.

var halogens = {'fluorine', 'chlorine', 'bromine', 'iodine', 'astatine'};

var elements = <String>{}; 
elements.add('fluorine'); 
elements.addAll(halogens);

• To create an empty set, use {} preceded by a type argument, or assign {} to a variable of type Set.

  var names = <String>{}; 
  // Set<String> names = {}; // This works, too. 
  // var names = {}; // Creates a map, not a set

  Note:

  Set or map? The syntax for map literals is similar to that for set literals. Because map literals came first, {} defaults to the Map type. If you forget the type annotation on {} or the variable it’s assigned to, then Dart creates an object of type Map<dynamic, dynamic>.

• Use .length to get the number of items in the set.

  assert(elements.length == 5);

• Sets support spread operators (... and ...?) and collection ifs and fors, just like lists do.