Accept only specified arguments in a function or class method

There are times that I’ve needed to limit input into a class method or function while using the extract() function. Problems arise at times from rogue argument keys that aren’t necessarily needed. Here’s a simple way to use the awesomeness of extract(), but dictate its output to the parameters of your allowed vars.

$allowed_vars('foo', 'bar', 'foobar'); 

# Set allowed vars as $ variables

# Extract only allowed vars from user-submitted arguments
# EXTR_IF_EXISTS will only convert array keys of foo, bar, and foobar
extract($args, EXTR_IF_EXISTS);