Why isn't 'false' equal to 'nil'? - ruby

Question

false is not equal to nil, for example:
false == nil # => false
The same goes for false and 0:
false == 0 # => false
You get the same result for nil and 0:
nil == 0 # => false
Why does Ruby act like this?

Answer 1

In Ruby, the only time nil will return true on a == comparison is when you do: nil == nil
You can read more about nil here:
https://ruby-doc.org/core-2.2.3/NilClass.html
nil is the equivalent of undefined in JavaScript or None in Python
Consider in JavaScript:
>> (undefined === false)
=> false
Or Python:
>> (None == False)
=> False

Answer 2

Nil and False (Equality)
Despite what many people new to the language may expect, nil and false are objects rather than language keywords. Consider FalseClass which says:
The global value false is the only instance of class FalseClass and represents a logically false value in boolean expressions.
Likewise, NilClass is:
[t]he class of the singleton object nil.
When you use a method like Comparable#== to compare them, Ruby invokes the spaceship operator <=> on the instances since neither class defines the #== method. Because nil and false are not the same objects, and because neither overrides the basic equality operator, the expression false == nil will always be false.
Likewise, an Integer like 0 is neither an instance of FalseClass nor NilClass. Both false == 0 and nil == 0 are therefore also false because neither instance evaluates to zero.
Truthy and Falsey (Conditionals)
For branching purposes, both false and nil evaluate as false in a conditional expression. Everything else evaluates as true.
Consider the following non-idiomatic, contrived, but hopefully illustrative example of Ruby's basic truth tables:
def truth_table value
if value
true
else
false
end
end
truth_table nil
#=> false
truth_table false
#=> false
truth_table true
#=> true
truth_table 'a'
#=> true
truth_table 0
#=> true
truth_table 1
#=> true
Boolean Evaluation
Nil and false are semantically different in Ruby, and descend from different base classes. They are also not equal to each other. However, they can both be treated as "not true" for branching purposes or within a Boolean context. For example, consider the following idioms for casting a result as a Boolean true or false value:
!(nil)
#=> true
!!(nil)
#=> false
You can use this idiom to shorten the previous truth table example to:
# Convert any value to a Boolean.
def truth_table value
!!value
end
# Test our truth table again in a more compact but less readable way.
table = {}
[nil, false, true, 'a', 0, 1].map { |v| table[v] = truth_table(v) }; table
#=> {nil=>false, false=>false, true=>true, "a"=>true, 0=>true, 1=>true}