Ruby number equal?

Question

Two number compare, like below:

#!/usr/bin/ruby

a=1000, b=1000, c=1000, d=1000
puts a==b, c==d

but print:

false
true

Why Ruby compare result like this?

Answer 1

Ruby's shortcut for setting multiple variables on one line is a little different than C-esque languages.

As pointed out in SimpleLime's Answer, the syntax you are using actually creates an array of the a variable.

As another pointed out in comment, the way your example is written would evaluate to the following:

a = [1000, (b = 1000), (c = 1000), (d = 1000)]

While b, c, and d set as expected, a does not. a is set to an array, while b, c, and d are set to 1000, since variable = value is actually a method call that returns the given value.

The Ruby syntax for what you really intended would look like this:

a, b, c, d = 1000, 1000, 1000, 1000

or what it actually evaluates to:

a, b, c, d = [1000, 1000, 1000, 1000]

You can also still do the other shortcut syntax that is pretty common if all the values are the same.

a = b = c = d = 1000

But beware of this syntax if not using "value" types, such as numerics or booleans, as all the objects will share the same reference.

Answer 2

In ruby you don't need the square brackets [] to create an array. So your variable creation line isn't doing what you think:

a=1000, b=1000, c=1000, d=1000
p a # [1000, 1000, 1000, 1000]
p b # 1000
p c # 1000
p d # 1000

So then, a == b is comparing the array [1000, 1000, 1000, 1000] == 1000, which is obviously false