Generic way to replace an object in it's own method

Question

With strings one can do this:

a = \"hello\"
a.upcase!
p a #=> \"HELLO\"

But how would I write my own method like that?

Somethin

Answer 1

Many classes are immutable (e.g. Numeric, Symbol, ...), so have no method allowing you to change their value.

On the other hand, any Object can have instance variables and these can be modified.

There is an easy way to delegate the behavior to a known object (say 42) and be able to change, later on, to another object, using SimpleDelegator. In the example below, quacks_like_an_int behaves like an Integer:

require 'delegate'
quacks_like_an_int = SimpleDelegator.new(42)
quacks_like_an_int.round(-1) # => 40
quacks_like_an_int.__setobj__(666)
quacks_like_an_int.round(-1) # => 670

You can use it to design a class too, for example:

require 'delegate'
class MutableInteger < SimpleDelegator
  def plus_plus!
    __setobj__(self + 1)
    self
  end

  def positify!
    __setobj__(0) if self < 0
    self
  end
end

i = MutableInteger.new(-42)
i.plus_plus! # => -41
i.positify! # => 0