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Project: Custom Enumerables


You should be very familiar with the Enumerable module that gets mixed into the Array and Hash classes (among others) and provides you with lots of handy iterator methods. To prove that there’s no magic to it, you’re going to rebuild those methods.


This project is a great opportunity to get comfortable using yield and the #call methods.

For this assignment, you will add your new methods onto the existing Enumerable module. Ruby makes this easy for you because any class or module can be modified by doing something like this:

  module Enumerable
    def my_each
      # your code here

For each method, create a script to compare your method to Ruby’s enumerable method, such as:

puts "my_each vs. each"
numbers = [1, 2, 3, 4, 5]
numbers.my_each  { |item| puts item }
numbers.each  { |item| puts item }
  1. Create #my_each, a method that is identical to #each but (obviously) does not use #each. You’ll need to use a yield statement. Make sure it returns the same thing as #each as well.
  2. Create #my_each_with_index in the same way.
  3. Create #my_select in the same way, though you may use #my_each in your definition (but not #each).
  4. Create #my_all? (continue as above)
  5. Create #my_any?
  6. Create #my_none?
  7. Create #my_count
  8. Create #my_map
  9. Create #my_inject
  10. Test your #my_inject by creating a method called #multiply_els which multiplies all the elements of the array together by using #my_inject, e.g. multiply_els([2,4,5]) #=> 40
  11. Modify your #my_map method to take a proc instead.
  12. Modify your #my_map method to take either a proc or a block. It won’t be necessary to apply both a proc and a block in the same #my_map call since you could get the same effect by chaining together one #my_map call with the block and one with the proc. This approach is also clearer, since the user doesn’t have to remember whether the proc or block will be run first. So if both a proc and a block are given, only execute the proc.
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