[Ruby] What is true?

I've been reading a technical book recently, and I think I understand it, I decided to output even the smallest details frequently.

This is an article for myself in the future.


In Ruby all values ​​except false and nil are true.

True and False

In Ruby, all data / values ​​are objects that belong to some class. Of course, true and false are no exception.

irb> true.class
=> TrueClass
irb> false.class
=> FalseClass

irb> true.class.ancestors
=> [TrueClass, Object, Kernel, BasicObject]
irb> false.class.ancestors
=> [FalseClass, Object, Kernel, BasicObject]

If all but false and nil are true, then 0 and (empty string) are also true.

#"0" is true
irb> p 0 ? true : false
=> true

#"" Is also true
irb> p '' ? true : false
(irb):15: warning: string literal in condition
=> true

However, in other languages ​​"0" is often false, and in JavaScript 0 and empty strings are falsy.

nil and false

There is a nil? Method to distinguish between nil and false.

irb> a = nil
=> nil
irb> a.nil?
=> true
irb> b = false
=> false
irb> b.nil?
=> false

When writing a Ruby program, nil may be mixed unexpectedly, so I often check nil, You can avoid nil objects by performing type conversion.

irb> nil.to_s
=> ""
irb> nil.to_i
=> 0
irb> nil.to_a
=> []
irb> nil.to_h
=> {}
irb> nil.to_sym
NoMethodError (undefined method `to_sym' for nil:NilClass)

to_sym is useless.


I was confusing true/false with true/false in Ruby, but the following article was very helpful. Ruby true/false is different from true/false

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