Ruby Tidbit: Super and Parameter Reassignment

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Something I've always loved about Ruby is that no matter how long I've been using it, it continues to surprise and delight me with neat little tricks. Here's one I was really surprised I never knew until now:

Let's say you want to enforce some kind of parameter formatting on an inherited method. You probably already know that you can write something like:

def my_nifty_method(value)
  super(nifty_parameter_formatter(value))
end

But, did you know that you can also do this?

def my_nifty_method(value)
  value = nifty_parameter_formatter(value)
  super
end

I didn't, until I just gave it a try this evening, for giggles. I figured it might work for methods that mutate an object, like Array#unshift, but since variable assignment is creating a new reference, I just assumed I'd need to explicitly pass in my modified value. Chalk me up as pleasantly surprised! Since I don't ever remember seeing this information before, and a few quick Google searches turned up empty, I thought I'd share.

[Update: I've been informed this specific behavior was one of the topics covered in James Edward Gray II's (aptly named) talk, "10 Things You Didn't Know Ruby Could Do". Worth a look for some other nifty tricks!]

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