Ensure with no rescue

1 minute to read

Need to ensure some code runs no matter what happens? Even with exceptions and returns? I’ve got just the under-documented feature for you! Ensure! Ensure, you say? Yip, let’s take a look.

Begin, Rescue, Ensure

I am sure most people have seen the typical usage of ensure, you toss it at the end of a being/rescue statement to make sure a snippet of code is always run. Ensure is good for things like making sure file descriptors are closed, boolean switches are flipped, etc. What happens if you still want the exceptions thrown?

Show me the code!

First, let us take a look at the basic being/rescue/ensure example:

Now, we’ll take out the rescue clause to ensure our exceptions bubble up and can be caught with whatever exception tracker we use.

With the rescue out, we get a closer to what we want, the exception is thrown but the code still cleans up our boolean switch.

What happens if we need to return out of the method based on a logic condition? Let’s see:

Oops, we left our boolean switch marked as running. Perhaps we use the ensure call on the method definition level:

Bingo! That is exactly what we wanted. Using ensure on the method definition level makes sure we always have our clean up code running, no matter what happens in the method. I found this interesting and under-documented so I wanted to share a detailed example.

Josh Owens

It all started with an Atari 800XL, but now Josh is a ruby and javascript developer with 10 years of professional experience. His current love is React.js, which he works with daily.