tag ruby, quick tip, regular expressions, case

Ruby Quick Tip: Regular Expressions in Case Statements

Did you know that you can use regular expressions in case statements in Ruby to check for a match? For instance, if I’m implementing some method_missing functionality and I want to check for bang or question methods, I might be tempted to do something like this:

def method_missing(name, *args)
  name = name.to_s
  if name.match(/!$/)
    puts "Bang Method!"
  elsif name.match(/\?$/)
    puts "Query Method?"
  else
    super
  end
end

But it’d be much cleaner if instead it looked like this:

def method_missing(name, *args)
  case name.to_s
    when /!$/
      puts "Bang Method!"
    when /\?$/
      puts "Query Method?"
    else
      super
  end
end

This is great, but now what if we want to call out a method for bang and question methods? Thankfully Ruby has us covered there as well:

def method_missing(name, *args)
  case name.to_s
    when /^(.*)!$/
      bang_method($1)
    when /^(.*)\?$/
      question_method($1)
    else
      super
  end
end

By using the $1 global variable we can access the last regular expression match performed by ruby. This is just one of those little details that makes working with Ruby such a joy.