Class Refinement

Class refinement is the Nit way to do open classes. The principle is basic: a Module can refine a class to improve it (the correct world might be "extend" but it could be misinterpreted because of Java).

To refine a class, use the keyword redef.

redef class String
    fun ellipsis(length: Int): String
    do
        if self.length <= length then return self
        return self.substring(0, length) + "..."
    end
end

print "hello world!".ellipsis(4) # -> "hell..."

Note that all classes can be refined, even primitive ones because Everything Is An Object.

Once a class is refined, all its instances and all its sub-classes gains the refinement.

Refinement can also be used to:

• redefine an existing method
• add attributes
• add new super-classes

When should I do refinement and when should I do specialization?

It is a tricky question since the best answer depends on the concrete usecase and problem. However, there is a good rule of thumb: If you hesitate between refinement and specialization, then it is specialization.