Question

I thought that by convention, only methods with an exclamation mark altered the object.

> array = [1, 2, 3]
 => [1, 2, 3] 
> array.pop
 => 3 
> array
 => [1, 2] 

Why isn’t Array‘s pop method called pop!?

Answer 1

That’s not quite correct.

From The Ruby Style Guide

The names of potentially "dangerous" methods (i.e. methods that modify self or the arguments, exit! (doesn’t run the finalizers like exit does), etc.) should end with an exclamation mark if there exists a safe version of that dangerous method.

And the name of pop method says exactly what it is doing so there’s no need to sign it with exclamation mark.