CSC/ECE 517 Fall 2007/wiki1b 1 c4

Introduction

Problem

If multiple methods with the same name are defined, there needs to be some way of determining which method a call refers to. The general rule is given on p. 123 of Programming Ruby. But questions still remain.

Questions

• Is it possible to get unexpected behavior if one of the modules you are using is "enhanced" to contain a new method that happens to conflict with a name of an existing method?
• Is it possible to refer to these methods using a qualified name?
• Is it possible to use method aliasing to resolve the ambiguity?
• What approach does good o-o design dictate?

Method

What is it?

A section of code that does or performs a task and then returns a value. A synonym for a method is a function. Methods can also be included within classes and used as accessors, mutators and setters.[2] Methods are created with the keyword def and the name of the method and end with the keyword end. A method is called by simply typing the name of the method and enclosing any parameters to the method in "()". i.e. some_method(some_parameter).[1]

General Rule For Multiple Methods

If multiple methods with are defined with the same name and a call is made to that method, Ruby will look in the immediate class of an object first for the method definition. It then will look in any mixins included within the class and lastly in any superclasses and their mixins. If multiple mixins are present the rule for searching is that the last one included will be search first.[1]

Resolving Ambiguity with Method Aliasing

It Is Possible

It is possible to use method aliasing to resolve ambiguity. The odds of a class having a method with the same name is very small. However aliasing will take care of if a module is included and the module includes a method that has the same name as a method within the class. You would now simply refer to the method in the class by the alias method and ambiguity is solved because the class definition is now independent on whether the module methods are aliased or not.

To truly take out all ambiguity you would need to also alias all methods within the module. If this is done properly then the multiple method rule will not need to be used. Each method in both modules and classes would be referenced by there alias name which will point it to the correct method. The class could now have any number of modules included or any number of superclasses and still keeping with good object oriented programming.[4]

Negatives

• Copies are created for each method that is aliased.[3] If you have 100 modules and 200 classes with 20 methods in each, then instead of 4000 methods you not have 8000 methods that have been defined and only half are unique. This is not good.

• If you are dealing with a large scale ruby project the number of aliases you have to deal with is enormous. Simply giving more descriptive method names would work better.

References

1. Programming Ruby: The Pragmatic Programmers' Guide
2. http://en.wikibooks.org/wiki/Programming:Ruby_Method_Calls
3. http://ruby.about.com/od/learnruby/qt/using_alias.htm