Is Ruby Range comparison implemented incorrectly?

Question

As in the documentation, two ranges that represent the same elements are considered different:

(1..2).to_a # => [1, 2] 
(1...3).to_a # => [1, 2] 
(1..2) == (1...3) # => false 

Why are two ranges that represent the same elements are considered different? I don't think that's how it works in math though.

In PostgreSQL, it is implement correctly:

test=# select int4range(1,2, '[]') = int4range(1,3, '[)');
 ?column? 
----------
 t
(1 row)

Answer 1

These ranges aren't equal - consider the case when you call include? with a floating-point value:

(1 .. 2).include? 2.5
false

(1 ... 3).include? 2.5
true

They happen to return the same results if you compare them to integers, but that doesn't mean they're identical.