Difference between '..' (double-dot) and '…' (triple-dot) in range generation?

Question

I\'ve just started learning Ruby and Ruby on Rails and came across validation code that uses ranges:

validates_inclusion_of :age, :in => 21..99
validates_         


        

Answer 1

a...b excludes the end value, while a..b includes the end value.

When working with integers, a...b behaves as a..b-1.

>> (-1...3).to_a
=> [-1, 0, 1, 2]

>> (-1..2).to_a
=> [-1, 0, 1, 2]

>> (-1..2).to_a == (-1...3).to_a
=> true

But really the ranges differ on a real number line.

>> (-1..2) == (-1...3)
=> false

You can see this when incrementing in fractional steps.

>> (-1..2).step(0.5).to_a
=> [-1.0, -0.5, 0.0, 0.5, 1.0, 1.5, 2.0]

>> (-1...3).step(0.5).to_a
=> [-1.0, -0.5, 0.0, 0.5, 1.0, 1.5, 2.0, 2.5]