Testing

see the resources at the bottom of this doc

Your task is to complete the code in your_code_here.rb to make the existing tests in enumerable_test.rb to pass.

The code is for you to reimplment all of Enumerable but only using each -- All of Ruby's Enumerable features can, and likely are, implemented internally (by Matz and the other core maintainers) in terms of each

This will also be excellent practice in reviewing Enumerable

I have given you one example of select tests and an implementation. I have also given a Book class to be found in lib/book.rb. I have also disallowed any Enumerable method other than each - bwahahahaha -- after all, it is your goal to write them from scratch.

For the remainder of the tests, one at a time, remove the skip instruction from one test. Then write the code in your_code_here to make that pass. Try taking small steps. First define the method, then start filling it in.

Example

You will notice in the select example the keyword yield -- In this type of code the yield means execute the block of code (the stuff in the test within the {}) and the arguments to the yield become the arguments to the block.

Lets break down the select test and example.

  it "implements select correctly" do
    short_books = [@h2g2, @pride]

    assert_equal short_books, @reimplements_enumerable.select { |book| book.page_count < 500 }
  end

This says that if we ask @reimplements_enumerable to select only the books that are less than 500 pages (e.g. @reimplements_enumerable.select { |book| book.page_count < 500 } we get the two books, @h2h2, and @pride. Since those books are short.

Lets look at the implementation

  def select
    result = []

    @collection.each do |element|
      should_select = yield(element)
      if should_select
        result << element
      end
    end

    return result
  end

We start by making an empty array named result, next we use each to go through the @collection (that represents all the elements)

While going through each element we first yield that element to the block and see what we get back. We store that boolean in a variable named should_select

If should_select is true, then we put that element at the end of the array via the << (shovel) operator.

After going through all the elements we return the result array.

Explorer Mode

Complete all the tests that have skip statements. Remove the skip one at a time until you have that test passing. If you get stuck, put the skip back in and move to a different test.

Adventure Mode

Some enumerables are noted at the bottom of the file without any tests. Write test and code for those.

Epic Mode

Seak out some other enumerable methods not mentioned here (See the docs) and write tests and code for those.

Resources

• Ruby Blocks / Yield
• Enumerable