FAQ: Blocks, Procs, and Lambdas - Keeping Your Code DRY

This community-built FAQ covers the “Keeping Your Code DRY” exercise from the lesson “Blocks, Procs, and Lambdas”.

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Learn Ruby

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Bonjour !
Merci pour le cours de Ruby, très ludique et facile à comprendre.

I have an issue with Proc
I don’t really understand how the Proc works.

multiples_of_3 = Proc.new do |n|
n % 3 == 0

print (1…100).to_a.select(&multiples_of_3)

How can we write the same thing without the Proc?

Hi, Just to reply the question you defined in English, it would look like this -

print (1...100).to_a.select {|n|
   n % 3 == 0

Without procs we are just passing a block of code to the method “select” here.
To put DRY in place, we would want to use procs, that would just replace the block of code with the variable that stores the block of code.
You can call the same using “&” notation.

print (1…100).to_a.select(&multiples_of_3)

Correct me if I am wrong, I am still new, learning Ruby and its fun so far. Hope you find this explanation useful.


Can anyone explain why we use to_a in this example? Calling print (1..100).select(&multiples_of_3) without .to_a seems to return the same result (still an array of numbers) and I’m curious the reasoning for this as I’m new to Ruby.

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I believe you have a point here! Let me explain:


.to_a converts the Range 1…100 into an Array that represents that range. That short conversion method returns a new object of a specific class that represents the current object.


.select() is a Array class method which returns a new array containing all elements of array for which the given block returns a true value. The syntax is: Array.select().
The #select method is part of the Enumerable ruby module, which is a collection of iteration methods.

Last but not least:


A range (1…100) is an object which has a starting value & ending value. Interesting enough, the Range class includes Enumerable, so you get all the powerful iteration methods without having to convert the range into an array and then the .select() method returns a new array. So .to_a is not needed! Plus the code executes much faster without it, but that’s another story :wink:

Hence to conclude I believe the .to_a method is redundant here :slight_smile:

1 Like