Wednesday, February 17, 2010

Ruby and Simple Dynamic Programming V

I've been reading Paolo Perrotta's new book "Metaprogramming Ruby" recently and enjoying it thoroughly. In the first chapter, he talks about Monkey Patching, the ability to add methods to classes at runtime. This combined with a need recently for an iterator through an array that returns both the index and the value led me to come up with the following code:

# Open the Array class and add a new method "each_with_index".
# This will loop through the array using the each_index method
# and yeild the index and the value of the array at that index.
class Array
def each_with_index
self.each_index do | i |
yield i, self[i]


# Create a simple array
x = [ "hello", "world", 42, 3.14159, ["test", "an", "array"] ]

# Go through the array and print each index and value in the
# array.
x.each_with_index do | i, v |
puts "index = #{i} value = #{v}"


The code is pretty simple. We open the Arrary class, define the new method, and then close the class. There's a bit of test code after that to show that everything works as expected.

Even though I'm only through the first chapter, I can recommend Perrotta's book. It's an easy read (so far anyway) and clearly shows the concepts that it discusses. The form it takes is conversational and the narrative is that you're a programmer, new to Ruby, who is paired with a senior developer Bill. This format may not be for everyone, especially if you're looking for more "formality", but I think it works well here and it's not overdone.

Let me know if you have questions or comments.


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  3. You know Enumerable has #each_with_index right? :P

    Either way it's cool, I've been contemplating getting the book for a while. Looks like a good read.