What is the purpose of “!” and “?” at the end of method names?

Question

Sometimes I see methods in Ruby that have \"?\" and \"!\" at the end of them, e.g:

name = \"sample_string\"
name.reverse
name.reverse!
name.is_binary_data?
<         


        

Answer 1

Beware, this isn't always the case. Take for example, Ruby Array#concat http://docs.ruby-lang.org/en/2.0.0/Array.html#method-i-concat.

Where you can get burnt badly is something like MyActiveRecordModel.column_names.concat([url]). Later calls related to MyActiveRecordModel will try to look for a column of 'url' for MyActiveRecordModel and throw.

Instead you must clone it before doing the concat. Fortunately my test suite caught this one, but.. heads up!