[bluesnowmonkey]

Having recently worked with a Ruby codebase where anything could be nil at anytime, I consider even references to nil to be a code smell. Developers are inherently prone to ignoring error handling, so they'll happily ignore the fact that Order#customer really means Order#customer_or_nil. And when they see errors in production, they'll slap an andand on it and call it fixed. The code becomes extremely difficult to reason about.

I prefer that functions throw an exception when unable to do what they promised, rather than return nil or a null object. The try-catch block serves as documentation that the function might fail. If someone forgets to catch the exception, it will shut everything down rather than leave the program in an unanticipated state that could lead to an error elsewhere.

[DanielRibeiro]

Nils are a very bad code smell. They come from C's null, which is a billion dollar mistake[1], according to its creator: Tonny Hoare. Specially now that we have monads[2, 3].

Scala's standard library provides very helpful information on how to replace null with its Maybe class (called Option in Scala). Just take a peek into their collections library[4], and search for Option.

[1] http://www.infoq.com/presentations/Null-References-The-Billi...

[2] http://moonbase.rydia.net/mental/writings/programming/monads...

[3] http://andand.rubyforge.org/

[4] http://www.scala-lang.org/api/current/scala/collection/immut...

[aphyr]

Nils are a very bad code smell. They come from C's null, which is a billion dollar mistake[1], according to its creator: Tonny Hoare. Specially now that we have monads[2, 3].

Do you have a source for this? I was under the impression nil was directly taken from Smalltalk, which derived it from Lisp.

[DanielRibeiro]

Wikipedia[1] has the refs:

The null reference was invented by C.A.R. Hoare in 1965 as part of the Algol W language. Hoare later (2009) described his invention as a "billion-dollar mistake":[10][11]

[1] http://en.wikipedia.org/wiki/Null_pointer#Null_pointer

Where:

[10] http://qconlondon.com/london-2009/presentation/Null+Referenc...

[11] http://www.infoq.com/presentations/Null-References-The-Billi...

Yes, the same video I linked above.

[aphyr]

Nil was a part of Lisp 1, which is why I was confused. It predates Algol W by seven years. As null references and nil are somewhat different beasts, I'm not sure the criticism "billion dollar mistake" applies fully.

[sdevlin]

This is something that's nice about ML-family languages. Data is not "nullable" by default. If you want to introduce that possibility, you need to wrap it in some form of "option" type - and you're forced to deal with the consequences of that explicitly.