Trait (computer programming)

In computer programming, a trait is a concept used in object-oriented programming, which represents a set of methods that can be used to extend the functionality of a class.

Traits both provide a set of methods that implement behaviour to a class, and require that the class implement a set of methods that parameterize the provided behaviour.

For inter-object communication (and sharing between objects), traits are somewhat between an object-oriented and a mixin. An interface may define one or more behaviors via method signatures, while a trait defines behaviors via full method definitions: i.e., it includes the body of the methods. In contrast, mixins include full method definitions and may also carry state through member variable, while traits usually don't.

Hence an object defined as a trait is created as the composition of methods, which can be used by other classes without requiring multiple inheritance. In case of a naming collision, when more than one trait to be used by a class has a method with the same name, the programmer must explicitly disambiguate which one of those methods will be used in the class; thus manually solving the diamond problem of multiple inheritance. This is different from other composition methods in object-oriented programming, where conflicting names are automatically resolved by scoping rules.

Whereas mixins can be composed only using the inheritance operation, traits offer a much wider selection of operations, including:

Traits are composed in the following ways:

Traits come originally from the programming language Self and are supported by the following programming languages:

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