CODEWITHSUNDEEP
rubyclassnullboolean
iswg
iswg

Reputation: 195

Ruby writing type checker for booleans

I'm working on this exercise on Codewars (https://www.codewars.com/kata/typer-dot-js/), and I'm having trouble writing a type checker for booleans.

Based on my understanding, booleans either return true or false. But I've also read a lot of people saying that every object in Ruby is a boolean except for nil. I tried writing the method in a bunch of different ways, but I'm just not getting it. Below are some of the tries.

class Typer

def self.is_boolean? input
  input == true || false
end

def self.is_boolean? input
  input.class == TrueClass || FalseClass
end

def self.is_boolean? input
  input == nil ? false : true
end

Upvotes: 0

Views: 60

Answers (2)

BrunoF
BrunoF

Reputation: 3523

Ruby does not have a built-in method to convert values to Boolean. That may be by design, as the only false values in Ruby are false and nil. All other values (empty string, empty array, empty hash, 0) are true. There, however, a "hack" that can be used to convert values to Boolean: it’s called "bang-bang" or "double-bang" and it consists of two Boolean negation operators, like this:

!!nil
=> false

!!false
=> false

!!""
=> true

!!0
=> true

!![]
=> true

!!{}
=> true

Upvotes: 0

Yu Hao
Yu Hao

Reputation: 122383

|| doesn't work as you expected. For example, 

input == true || false

is testing if 

input == true

is truthy, or if 

false

is truthy. Note that the latter isn't testing input == false. And that is your main misunderstanding.

Upvotes: 2

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