Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In computer programming, a trait is a collection of methods, used as a "simple conceptual model for structuring object oriented programs". Traits are similar to mixins, but whereas mixins can be composed only using the inheritance operation, traits offer a much wider selection of operations, including symmetric sum, method exclusion, and aliasing. A Trait differs from an abstract type in that it provides implementations of its methods, not just type signatures. Traits are supported as a native language feature in the Fortress programming language (where they also play the role of types), in the Scala programming language, the Squeak version of Smalltalk from version 3.9, and in Perl 6 (which calls them "roles"), as an add-on by the Moose module for Perl 5 and the Joose framework for JavaScript, and have been proposed for inclusion in PHP[4] and ActionScript 3.0. Module mixins in Ruby are similar to traits to some degree.

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