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Since "this" in the body of a function is the reference to the object used to call the function, e.g.

obj.setProp = function(p) { this.prop = p }
obj.setProp(5)
obj.prop
=> 5

and since JavaScript constructor function is the same as any other JavaScript function -and the only difference that happens is through the use of the new operator-, we can use "this" to inject functionality provided by multiple constructor functions (sort of multiple inheritance) into our own objects. This can happen as long as these constructor functions are not only natively implemented (e.g. Array, String, Function, .... etc), and as long as the injected functionalites are not dependent on their prototypes.

One of the most powerful features of Rails is plugins; plugins enable developers to make generic extensions to Rails applications that others can benifit from. One can use two different approaches to add new logic/aspects to a Rails application through a plugin: metaprogramming and generators. This entry is not a tutorial about writing Rails plugins; assuming that you know the basics of metaprogramming in Ruby, and using a very basic example, we'll try to conduct a simple comparison between the two approaches that can be generalized.