Modifying argument in a Ruby method

Wed, 01 Jul 2026 08:33:20 +0000

If you’ve been working with Ruby for a while, you probably know that arguments are passed into methods by reference to the object (more specifically, pass-by-sharing). Because of this, you cannot simply reassign a new value to an argument inside a method and expect it to change outside. Technically, you can assign it, but once the method finishes execution, the outer variable will still hold its original value. For example:

def change(a)
  a = 'other string'
  nil
end

s = 'some string'
change(s)
puts s # some string

One way to solve this is to wrap the incoming parameter in a collection or create a custom wrapper class to encapsulate your value. To put it clearly, it looks something like this:

PassBySharing on Artem Yegorov

Modifying argument in a Ruby method