Returns true if 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.
The equality used to determine whether element is equal to an element of the iterable defaults to the Object.operator== 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.identical) that its contains
uses.
Likewise the Iterable
returned by a Map.keys call
should use the same equality that the Map
uses for keys.