With the official release of Ruby 2.0, there have been a myriad of posts about all of its shiny new features. Of those, my personal favorite is the addition of keyword arguments. This is essentially built-in support for what's been traditionally accomplished in Ruby using options hashes. For example, it's not uncommon to see method calls like foo(bar: "one", baz: "two"). However, under the hood this might be implemented as:

def foo(options={})
  bar = options.delete(:bar)
  baz = options.delete(:baz)
  puts "#{bar} #{baz}"

foo(bar: "one", baz: "two") # => "one two"

In fact ActiveSupport in Rails 3.2.13 defines a method called extract_options! that deals with exactly this. However, if we're stuck on Ruby < 2.0, defining every method to use an options hash is often more work than necessary, especially when a method only takes one or two parameters. We can get around this with a clever trick. If we change our method slightly from the previous example to work without an options hash:

def foo(bar, baz)
  puts "#{bar} #{baz}"

We can then fake keyword arguments by calling it like this:

foo(bar = "one", baz = "two")
# => "one two"

This trick exploits the fact that the returned value from the assignments in the call to foo() will be the value that's assigned, so at the end of the day "one" and "two" will still be passed in! This saves us having to work with options hashes and still looks pretty, although it's important to note that unlike hashes and Ruby 2 keyword arguments, order matters here. If you change up the order you pass in baz and bar, things won't work as expected.

Personally, I can't wait to switch my projects to use Ruby 2.0 and use keywords arguments for real, but in the mean time this is a neat trick I hadn't seen before to emulate them!

Tags: ruby