rb_str_modify() equivalent in the Ruby language

Question

I was trying to add a method to the String class. This method should mutate the current string (of course it would be possible to write a not mutating version but I'd prefer the mutating one). I had no idea how to do this and after some googling I found the method rb_str_modify which makes a given string mutable. That's exactly what I need but I couldn't find an equivalent in the Ruby language. Did I miss something or is there really no possibility in the language itself?

Answer 1

Reopening Classes

All classes in Ruby are open for extension so you can simply do this ...

Class String

    def my_new_method(args)

       # Some sort of modification to self

       self.replace "SOME CALCULATED VALUE"

    end

end

... somewhere in your code. I've modified string a few times in different applications - usually I just put the modifications into one particular module, making it easy to reuse them or remove them as required.

Modifying individual objects

Modifying a class in its entirety is dangerous as it's very difficult to identify all of the consequences - I once broke Merb by modifying a method in the String class. It's much safer to modify particular objects. This is easy in Ruby - you use the extend keyword. You define a module, add your function and then modify the target object. This example ...

module Humor
  def tickle
    "hee, hee!"
  end
end
a = "Grouchy"
a.extend Humor
a.tickle  »  "hee, hee!"

is taken from the Pickaxe book

Chris