Null Objects
Tom Locke and I have similar proclivities. He says:
class Object
def _?()
self
end
end
class NilClass
def _?()
SafeNil.new
end
end
class SafeNil
def method_missing(*args, &b)
nil.send(*args, &b) rescue nil
end
end
I say:
class Object
def null
n = nil
def n.method_missing(*args)
null
end
n
end
end
The difference:
string_or_nil._?.length # Tom's
(string_or_nil||null).length # mine
I like being able to go more than one method deep,
(string_or_nil||null).length * 4
But that might not be to your taste.
Nice. Is your line 4 supposed to read:
def n.method_missing(*args)
?
Yes thanks, fixed now. Also instead of Object.new the singleton object needed to be nil, to evaluate as false. Should have checked before typing.
I like how simple your implementation is compared to Tom’s.
Unfortunately, I believe it has a fatal flaw: As soon as you call null once, the NilClass is permanently changed and *all* nil objects will have this new “safe nil” behavior.
puts nil.foo rescue p $!
# => #
null
puts nil.foo rescue p $!
# => nil
I don’t really understand why it has to be this way, but I’m guessing it has to do with the fact that nil itself is a “singleton object” (according to http://corelib.rubyonrails.org/classes/NilClass.html)
Ah. I was wondering how long it would take you to work that out. :)
(http://www.imdb.com/title/tt0062552/quotes)
Let this be a lesson in how to shoot yourself in the foot with open core classes. Maybe I should be using Java so I don’t hurt myself.