A practical guide to Scala Traits

Trait


- has a super class of AnyRef 

- uses extends or with for inheriting a trait (with to inherit multiple traits) 

- defines a type 

- can be overridden using override keyword 


Trait vs Interface (Java) 


- trait can declare fields and main state 

- rich vs thin interfaces (every concrete method added to trait makes it richer) 


Trait vs Class 


- trait can NOT have any class parameters 

     trait doesn't support coding in this style: class Point(x: Int, y: Int)

- super calls are statically bound in classes, but dynamically bound in trait 

     super.toString is predicable in classes, but not in trait when mixing 


Ordered Trait 


Traits as stackable modifications 

- order of mixins: right most trait takes effect first 


When to use Trait? 


- If the behaviour will not be reused, then make it a concrete class 

- If it might be reused in multiple, unrelated classes, make it a trait 

- If you want to inherit from it in Java code, use an abstract class 

- If you plan to distribute it in compiled form, and you expect outside groups to write classes inheriting from it, you might lean towards using an abstract class 

- If efficiency is very important, lean towards using a class 

- If you still do not know, after considering the above, then start by making it as a trait 







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