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Programming in Scala, Second Edition by Martin Odersky, Lex Spoon, Bill Venners

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Chapter 12

Traits

Traits are a fundamental unit of code reuse in Scala. A trait encapsulates method and field definitions, which can then be reused by mixing them into classes. Unlike class inheritance, in which each class must inherit from just one superclass, a class can mix in any number of traits. This chapter shows you how traits work and shows two of the most common ways they are useful: widening thin interfaces to rich ones, and defining stackable modifications. It also shows how to use the Ordered trait and compares traits to the multiple inheritance of other languages.

12.1 How traits work

A trait definition looks just like a class definition except that it uses the keyword trait. An example is shown in Listing 12.1:

    trait Philosophical ...

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