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?

I was wondering what their purpose is? Are they just syntax sugarcoating?

Answer 1

It's "just sugarcoating" for readability, but they do have common meanings:

• Methods ending in ! perform some permanent or potentially dangerous change; for example:
  • Enumerable#sort returns a sorted version of the object while Enumerable#sort! sorts it in place.
  • In Rails, ActiveRecord::Base#save returns false if saving failed, while ActiveRecord::Base#save! raises an exception.
  • Kernel::exit causes a script to exit, while Kernel::exit! does so immediately, bypassing any exit handlers.
• Methods ending in ? return a boolean, which makes the code flow even more intuitively like a sentence — if number.zero? reads like "if the number is zero", but if number.zero just looks weird.

In your example, name.reverse evaluates to a reversed string, but only after the name.reverse! line does the name variable actually contain the reversed name. name.is_binary_data? looks like "is name binary data?".