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Ruby

Posted by Anthony Quisenberry
Anthony Quisenberry
13,074 Points

Why is Nil in the boolean discussion of ruby?

Why is Nill considered a boolean, or at least represented as a boolean value in the Boolean tutorial for ruby? By definition a booean, for the terms of computer science, is a "data type, having two values (usually denoted true and false), intended to represent the truth values of logic and Boolean algebra"

3 Answers

Geoff Parsons
Geoff Parsons
11,679 Points
Geoff Parsons
Geoff Parsons
11,679 Points

nil is one of the few other values that can be thought of as false similar to how in other languages 0 and 1 can be thought of false and true (respectively). So it's not a boolean itself but is useful to cover here regardless. In case you were wondering nil is of type NilClass.

  foo = nil
  if foo
    # this will never execute
  end
Anthony Quisenberry
Anthony Quisenberry
13,074 Points
Anthony Quisenberry
Anthony Quisenberry
13,074 Points

But isn't a boolean supposed to have its own binary. So would it be nil and exists? It just doesn't seem to follow the way that booleans work, at least to me.

Geoff Parsons
Geoff Parsons
11,679 Points

nil is certainly not a boolean, it is it's own special value that is used to represent null values. For example instance variables (e.g. @foo) will by default evaluate to nil if they have not previously been set. You can also specifically set a value to nil as I showed in the previous example. To be more clear and to explicitly check a boolean value you can use .nil? which returns true if the object is nil. This makes the code a little more understandable in some cases as well.

  foo = nil
  if foo.nil?
    # do something
  end
Anthony Quisenberry
Anthony Quisenberry
13,074 Points
Anthony Quisenberry
Anthony Quisenberry
13,074 Points

I cross posted this question on stack overflow and the answer I got there was very helpful in explaining it. Thought I would post that here in case other people who think like me might understand it better this way:

"Every expression in Ruby is being evaluated to an object and every object has a boolean value.

Many expressions can have a false value, but the only two objects in Ruby to have a boolean value of false are nil and false. That's why."