Ruby Idioms, Part 1

Written on 7:16:00 PM by S. Potter

With more people moving to Ruby everyday from languages like Java, I wanted to create blog entries on the most common Ruby idioms (especially ones frequently found in Rails core or Rails application code) and briefly explain how to convert your Java mindset to Ruby (over time). This is the first installment. First let us inspect what we might do in Java (converted to Ruby syntax) when determining if a value passed in equals various fixed values:

if val == 1 || val == 3 || val == 5
  puts "hello odd number under 7"
end

Rubyists will know this is really ugly, so our first attempt at Rubifying the code above would probably look like:

if [1, 3, 5].include? val
  puts "hello odd number under 7"
end

Of course, one-liner fans should note you can also do the following:

puts "hello odd number under 7" if [1, 3, 5].include? val

include? is an instance method on Array (which is a builtin Ruby class - remember all first class citizens in Ruby are classes [or more technically, modules]). In Ruby developers use "?" postfixes in method names as a way to letting clients of the method know it should return a true or false value. I described the unwritten/unofficial Ruby conventions and guidelines for naming in a previous blog entry Rubyisms: Naming Conventions This first attempt is fairly nice, because it makes (in my opinion) the code more readable and more like my natural language, English. Now it doesn't quite read as well as it could, so let's try again:

class Array
  alias :includes? :include?
end

if [1, 3, 5].includes? val
  puts "hello odd number under 7"
end
# OR the one-liner version
puts "hello odd number under 7" if [1, 3, 5].includes? val

The code snippet above reopens a class in Ruby, a facility I describe in a previous blog entry Rubyisms: Reopening Classes. You should refer to that for more information. Now some may be saying, "this is terrible...you have converted a 3 line code snippet into 6." Well not exactly. The reason is, the first three lines just need to be put in a ruby file to extend the Array class just once in the whole application, library or framework and you can use the aliased method, includes?, as many times as you like throughout the code base with not a care in the world. Of course there are a variety of ways to change the code to be more readable as per your opinion of code readability, but I'll leave that as an exercise for the reader. Ruby's core Range class could be used to generate an array of odd (or even) numbers under a specific number. Another blog entry will deal with this.

Posted in idioms, natural language, ruby, ruby idioms

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