In the last post I wrote about how I implemented a Hash with regex keys and lambda values. Here’s the desired output:

  • Strings beginning with ‘Foo’ => ‘group A’
  • Strings beginning with ‘F’ (but not ‘Foo’) => ‘group B’
  • Strings beginning with ‘Bar’ => ‘group C’
  • Strings beginning with ‘Baz’ => same string, but replace all ‘a’s with ‘0’s

Implementing this using case is pretty straightforward:

module StringLookup

  def self.lookup(string)
    case string
    when /^Foo.*$/ then 'group A'
    when /^F.*$/   then 'group B'
    when /^Bar.*$/ then 'group C'
    when /^Baz.*$/ then string.gsub('a', '0')


That’s it. No extra module, no mix-ins. All the original specs still pass with this code. This code is a bit more boring than the Hash code, but that’s a good thing. It’s a lot simpler, easier to read and understand, and there’s less to maintain.

I didn’t bother to profile the code since it wasn’t necessary for what it was going to be used for. Whatever performance advantage hashes could have offered, however, were probably negated by having to go over the keys to find a matching pattern.

All the code is in this gist. Note that to run the specs you will have to change the require 'string_lookup' and/or the method name in StringLookup.

“…she had never before seen a rabbit with either a waistcoat-pocket, or a watch to take out of it, and burning with curiosity, she ran across the field after it…”
Alice’s Adventures in Wonderland by Lewis Carroll