The One Thing You Need To Know About Bang Methods

You have probably stumbled across code like this (or maybe written it yourself):

subscription.cancel!

You likely took this as an indication of a method invocation with serious consequences. But what about this:

house.destroy

Hmmm. One would think that demolition of a house would qualify as a pretty serious. Why then, doesn’t #destroy end with a bang?

Let’s look at a few examples:

• Hash#delete
• Array#clear

No exclamations to be seen. Now let’s look at instances where a bang is actually used:

• Hash#merge
• Hash#merge!
• Array#map
• Array#map!

Or the example of a well known library:

• ActiveRecord::Persistence#save
• ActiveRecord::Persistence#save!

If you look at these carefully, you’ll notice 2 things:

1. There is a version of the method that doesn’t end with a bang, and one that does.

2. The method version ending with a bang doesn’t necessarily imply a more destructive behavior.

So when should you actually end a method with a bang?

You should do it only when you want to convey a slight variation in behavior versus the non-bang version—one that doesn’t justify giving the alternative version a completely different name.

There, now you know the secret. Now go forth and write more idiomatic Ruby. And stop writing all those annoying bangs!

—David Leal