Something is wrong with Ruby! The Enumerable methods that we know and love have stopped working (not really, but let's pretend).
Let's implement some of our favorite Enumerable methods (each, select, map, etc) without using any of
the built in methods that Ruby gives us. We will add g_ to the methods names
to make sure that we don't interfere with Ruby's built in methods.
In this exercise we are going to re-implement some of the methods that Ruby provides for us and that we commonly use:
- each
- select
- reject
- map
- find
- select!
Although both hashes and arrays are enumerable, we are going to focus only on arrays for this exercise. As you are going through the exercise, you may want to reference to the documentation for both Array and Enumerable to check the expected behavior of some of the methods we are going to be implementing:
Instead of using the same name that Ruby gives to these methods, we will add g_
to the beginning of each method so that we make sure not to clash with any of the
built in Ruby methods. For example, we will implement g_each, g_select, etc.
We are going to define our methods in a module called GschoolEnumerable. Check out
lib/gschool_enumerable.rb for the structure.
Modules, or mixins, allow us to define methods and then add those methods to other classes as desired. Here is an example:
module NameMethods
def full_name
"#{first_name} #{last_name}"
end
end
This module defines a method that assumes it has access to a first_name and last_name method. If you included this module in the following class
class Person
include NameMethods
attr_reader :first_name, :last_name
def initialize(first_name, last_name)
@first_name = first_name
@last_name = last_name
end
end
Then instances of the Person class would have respond to an instance method called
full_name
hunter = Person.new("Hunter", "G")
puts hunter.full_name # => "Hunter G"
Nice!
If you look at spec/lib/gschool_enumerable_spec.rb#4, you can see that in our
tests we are including the GschoolEnumerable module into the Array class. Once
we do that, we have access to all the instance methods we define in the
GschoolEnumerable class on each Array instance in our tests.