I'm pretty sure I saw on a Rails related site something along the lines of:

def my_function(*opts)
  opts.require_keys(:first, :second, :third)
end

And if one of the keys in require_keys weren't specified, or if there were keys that weren't specified, an exception was raised. I've been looking through ActiveSupport and I guess I might be looking for something like the inverse of except.

I like to try and use as much of the framework as possible compared to writing my own code, that's the reason I'm asking when I know how to make the same functionality on my own. :)

At the moment I'm doing it through the normal merge routine and making sure that I have what I need with some IFs.