The documentation for Range† says this:
Ranges constructed using
..
run from the beginning to the end inclusively. Those created using...
exclude the end value.
So a..b
is like a <= x <= b
, whereas a...b
is like a <= x < b
.
Note that, while to_a
on a Range of integers gives a collection of integers, a Range is not a set of values, but simply a pair of start/end values:
(1..5).include?(5) #=> true
(1...5).include?(5) #=> false
(1..4).include?(4.1) #=> false
(1...5).include?(4.1) #=> true
(1..4).to_a == (1...5).to_a #=> true
(1..4) == (1...5) #=> false
†The docs used to not include this, instead requiring reading the Pickaxe’s section on Ranges. Thanks to @MarkAmery (see below) for noting this update.