This document discusses Ruby equality and identity operators. It explains that equality refers to objects with the same value but different identities, while identity refers to variables referring to the same object. It then reviews several equality operators in Ruby: == tests for equal value, eql? tests for equal value and type, equal? tests for equal value, type and object identity. === is used like == in case statements, and =~ acts like a match method for Regexps. In conclusion, == is often sufficient but eql? and equal? can provide more precision, === enables elegant case statements, and =~ allows concise Regex testing.

1. Equality in
Ruby
Romain Sempé
@rsempe

2. Equality or Identity?
— Equality:
Different objects that represent the same value.
— Identity:
Different variables that refer to the same object.

3. Equal yes! But in what sense?
— What equality methods should we use?
— ==
— eql?
— equal?
— ===
— =~

4. ==
Test only if the objects have the same value.

5. eql?
Test if the objects have the same value and the
same type.

6. equal?
Test if the objects have the same value, the same
type and are the same instance in memory.

7. ===
Same as == but for case statements.
One operator depending on the context of the
comparison (Class, Range, Regexp, …).

8. =~
Interesting with the Regexp class.
It’s an alias to the match method.

9. Conclusion
— == is great most of the time
— eql? and equal? can be useful to be more precise
— Elegant case statements with ===
— Concise test for Regexp with =~
— Only one identity operator: equal?