# contains method

1. @override

bool contains(

1. Object? element

)
override

Whether the collection contains an element equal to `element`.

This operation will check each element in order for being equal to `element`, unless it has a more efficient way to find an element equal to `element`. Stops iterating on the first equal element.

The equality used to determine whether `element` is equal to an element of the iterable defaults to the Object.== of the element.

Some types of iterable may have a different equality used for its elements. For example, a Set may have a custom equality (see Set.identity) that its `contains` uses. Likewise the `Iterable` returned by a Map.keys call should use the same equality that the `Map` uses for keys.

Example:

    final gasPlanets = <int, String>{1: 'Jupiter', 2: 'Saturn'};
    final containsOne = gasPlanets.keys.contains(1); // true
    final containsFive = gasPlanets.keys.contains(5); // false
    final containsJupiter = gasPlanets.values.contains('Jupiter'); // true
    final containsMercury = gasPlanets.values.contains('Mercury'); // false

## Implementation

    @override
    bool contains(Object? element) {
      if (element is! E) return false;
      return _elements.contains(element);
    }