Difference between .. and ... in Ruby

Question

What is the difference between .. and ... in a ruby for loop.

for num in 1..5
    puts num
end

vs

for num in 1...5
    puts num
end

How are those two loops different.

score 1 · Answer 1 · answered May 01 '16 at 06:42

1

The three dots indicates that the end stops before the terminator, two dots indicates it includes the terminator.

1...5 -> 1 to 4

1..5 -> 1 to 5

answered May 01 '16 at 06:42

Pedro Lobito

In addition, there's a big difference between using two dots and three dots with Ruby's [flip-flop operator](https://blog.newrelic.com/2015/02/24/weird-ruby-part-3-fun-flip-flop-phenom/). :-) – Cary Swoveland May 01 '16 at 07:04

score 1 · Accepted Answer · answered May 01 '16 at 06:43

1

In ruby 1...5 gives you a range which doesn't include 5 whereas 1..5 gives you a range which does include 5

eg:

>> (1..5).to_a
[
    [0] 1,
    [1] 2,
    [2] 3,
    [3] 4,
    [4] 5
]
>> (1...5).to_a
[
    [0] 1,
    [1] 2,
    [2] 3,
    [3] 4
]

answered May 01 '16 at 06:43

Alfie

score 0 · Answer 3 · answered May 01 '16 at 06:42

0

The difference is between inclusive and no inclusive ranges.

i.e.:

(1..5).to_a
# => [1, 2, 3, 4, 5]
(1...5).to_a
# => [1, 2, 3, 4]

For this reason, your loops will have a different number of cycles.

answered May 01 '16 at 06:42

Myst

3 Answers3