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Every object in Ruby has a boolean value, meaning it is considered either true or false in a boolean context. Those considered true in this context are “truthy” and those considered false are “falsey.” In Ruby, only false and nil are “falsey,” everything else is “truthy.”
However, in terms of how it's implemented, nil is fundamentally different than in other languages. In Ruby, nil is—you've guessed it—an object. It's the single instance of the NilClass class. Since nil in Ruby is just an object like virtually anything else, this means that handling it is not a special case.
That's the easy part. In Ruby, you can check if an object is nil, just by calling the nil? on the object... even if the object is nil. That's quite logical if you think about it :) Side note : in Ruby, by convention, every method that ends with a question mark is designed to return a boolean (true or false).
In Ruby, nil is a special value that denotes the absence of any value. Nil is an object of NilClass. nil is Ruby's way of referring to nothing or void.
unless discount.nil? || discount == 0 # ... end
class Object
def nil_zero?
self.nil? || self == 0
end
end
# which lets you do
nil.nil_zero? # returns true
0.nil_zero? # returns true
1.nil_zero? # returns false
"a".nil_zero? # returns false
unless discount.nil_zero?
# do stuff...
end
Beware of the usual disclaimers... great power/responsibility, monkey patching leading to the dark side etc.
ok, after 5 years have passed....
if discount.try :nonzero?
...
end
It's important to note that try is defined in the ActiveSupport gem, so it is not available in plain ruby.
From Ruby 2.3.0 onward, you can combine the safe navigation operator (&.) with Numeric#nonzero?. &. returns nil if the instance was nil and nonzero? - if the number was 0:
if discount&.nonzero?
# ...
end
Or postfix:
do_something if discount&.nonzero?
unless [nil, 0].include?(discount) # ... end
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