Define a method that is a closure in Ruby

Question

I\'m re-defining a method in an object in ruby and I need the new method to be a closure. For example:

def mess_it_up(o)
  x = \"blah blah\"

  def o.to_s
    pu         


        

Answer 1

This seems to work.

class Foo
  def mess_it_up(o)
    x = "blah blah"

    o.instance_variable_set :@to_s_proc, Proc.new { puts x }
    def o.to_s
      @to_s_proc.call
    end
  end
end

var = Object.new
Foo.new.mess_it_up(var)

var.to_s

The problem is that code in def is not evaluated until it's run, and in a new scope. So you have to save the block to an instance variable on the object first and retieve it later.

And define_method doesn't work because it's a class method, meaning you would have to call it on the class of your object, giving that code to ALL instances of that class, and not just this instance.