What's the right way to implement equality in ruby
Solution 1:
To simplify comparison operators for objects with more than one state variable, create a method that returns all of the object's state as an array. Then just compare the two states:
class Thing
def initialize(a, b, c)
@a = a
@b = b
@c = c
end
def ==(o)
o.class == self.class && o.state == state
end
protected
def state
[@a, @b, @c]
end
end
p Thing.new(1, 2, 3) == Thing.new(1, 2, 3) # => true
p Thing.new(1, 2, 3) == Thing.new(1, 2, 4) # => false
Also, if you want instances of your class to be usable as a hash key, then add:
alias_method :eql?, :==
def hash
state.hash
end
These need to be public.
Solution 2:
To test all your instance variables equality at once:
def ==(other)
other.class == self.class && other.state == self.state
end
def state
self.instance_variables.map { |variable| self.instance_variable_get variable }
end