The Ruby Way (buy it at Amazon.com) is a Ruby programming book published by Addison-Wesley that’s often considered the “bible” of Ruby books. It covers a dizzying amount of Ruby topics in a “how to” format – including low level data types, metaprogramming, I/O, graphics libraries, Web development tools, OOP, IDEs, and more (see the full table of contents). It’s an essential book for any Rubyist’s library.

Where To Buy

Amazon typically offers the best price for The Ruby Way. Check it out on Amazon.com (US) or Amazon.co.uk (UK).

For example, let’s say your app is designed to run on multiple platforms, but a certain action has to be executed in a totally different way for a couple of platforms (a common situation where Windows is involved). You could define your logic like this:

if platform == Windows
  action1
elsif platform == Linux
  action2
else
  default_action
end

To this sort of arrangement Hal says: “Of course, there is a small runtime penalty for coding in this way since the flag may be tested many times in the course of execution.” He then presents a technique where a method itself is defined at run-time based upon the condition:

if platform == Windows
  def my_action
    action 1
  end
elsif platform == Linux
  def my_action
    action2
  end
else
  def my_action
    default_action
  end
end

To this, Hal says: “In this way, the same result is achieved, but the flag is only evaluated once; when the user’s code calls my_action, it will already have been defined appropriately.”

Personally I’m not entirely convinced by Hal’s specific example in The Ruby Way, but it’s a handy reminder of how dynamic Ruby is. I’m sure there are some great examples of this technique in the wild.

I believe there are three ways to do it (if you can think of any others, leave a comment!). Two reasonably obvious, but one that’s quite idiomatic (the one that The Ruby Way mentions):

1. str.empty? – With this we simply ask a String object if it’s “empty.”
2. str.length > 0 – With this we check whether the string has a length of more than zero – i.e. it’s not empty.
3. str[0] – With this we check the first character of the string. If no first character is present, both Ruby 1.8 and 1.9 return nil! This is particularly idiomatic and not something I’d considered before.

Of course, the shortest or most idiomatic route is not usually the best way to go when programming, but if you’re playing code golf, doing some obfuscation, or otherwise want to access the first character of the string anyway, option #3 is undeniably sneaky.

Note: Remember that while a string can only be empty or non-empty, a variable that you think is referring to a String object may well be nil! So often you need to check for nil as well as string length. You can do this with a simple if str or if str.nil?

print "Please enter a temperature and scale (C or F): "
str = gets
exit if str.nil? or str.empty?
str.chomp!
temp, scale = str.split(" ")

abort "#{temp} is not a valid number." if temp !~ /-?\d+/

The abort line threw me for a loop; I’d not seen it in use before. I jumped into irb to give it a try and, yes, it works and, yes, it’s documented:

Writing to STDERR can be pretty handy, especially if you’re a UNIX nerd threading together apps at the command line. So.. a nice find, even on such an early page of the book.