The redo Keyword in Ruby

Published in

RubyCademy

2 min readSep 10, 2018

In the following article, we’re going to explore the following topics:

redo for loops & enumerations

Ruby proposes a bunch of keywords that allow the developer to have control over loop & enumeration processing. This means that it can explicitly:

I prefer to talk about an iteration for a loop and a step for an enumeration.

In this article, we’ll keep our focus on the redo keyword.

Let’s see how the redo keyword works within a loop

Here we see that the first iteration is infinitely repeated.

This is due to the fact that we call the redo keyword and that the for condition is never evaluated — so the variable i is never incremented.

Note that After redo is never printed out because the redo keyword stops the iteration and starts the repetition the moment it’s called.

We just have to increment i to bypass the if i == 1 statement

Here the loop ends up naturally while the first iteration is repeated once because of the explicit incrementation.

It works pretty similarly for enumerations

redo doesn’t work only on iteration and enumeration.

Indeed, redo can also be used within a simple block. It’ll then rerun the block from the beginning

Here, the call to redo acts as a loop — an infinite loop in our case.

This is due to the fact that redo will rerun the block passed as an argument of the hello method.

NB: feel free to have a look to Method Arguments in Ruby: Part II article if you’re unfamiliar with Proc objects.

We could stop the infinite loop by adding a condition to our redo.

The redo keyword can be useful in the context of a loop or an enumeration.

Unfortunately, this tool is widely unknown or unused among Ruby developers.

Feel free to have a look at the Ruby tests (the redo_spec.rb file for example) to see some use cases for this keyword.

Also, feel free to let a comment to describe a real use case of this keyword that you’ve encountered during your developer’s journey. 🗺️

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