Numeric not operator trick

Explanation

(42 + 0.42).!@.!@

is equivalent to

!!(42 + 0.42)

The Double Negation idiom

Here's an interesting and somewhat popular idiom used to convert a value to a boolean (true or false).

This idiom is called Double Negation.

Let's see how it works:

!!42  # => true
!!nil # => false

!!true  # => true
!!false # => false

The code might look a bit mysterious, but once you realize that !@ is just a regular method in Ruby, double negation is essentially a shortcut for:

(42 + 0.42).!@.!@

It's crucial to note that !! is not some special operator; it's simply two negations combined. Some people find this confusing, so I wanted to clarify it here.

The !@ Unary operator

Calling 42.!.! is similar to calling 42.!@.!@, which is also similar to !!42.

They all invoke the BasicObject#!@ method.

The !@ is a convention to indicate that it's a unary method.

Here @ represents the receiver.

By convention, this lets other developers know that it's a unary method.

Resource

Unary operators in Ruby