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Not properly guarding for None has been over 2% of my bugs in working with Python. I'd guess it's more like 5-10%. There's probably another 5-10% that are pro

Not properly guarding for None has been over 2% of my bugs in working with Python. I'd guess it's more like 5-10%. There's probably another 5-10% that are problems dealing with trying to uniformly iterate over different kinds of structures, but I'm willing to admit I might just not know the correct way to do it (ie, map or fold or something).

actsasbuffoon 12y ago
The interesting thing is that the majority of statically-typed languages wouldn't catch the null for you. C, C++, Java, C#, and many others accept null as a valid input for any type. There are plenty of languages like Haskell, Haxe, Idris, Agda, Roy, Rust, and Elm that get this right. Anecdotally it seems that most developers who advocate static typing aren't using these languages. It seems like the majority are writing in one of the Algol derived languages from the first paragraph. Scala gets it half right with Option, but included null for Java compat. I've not written much Scala, but I've already encountered numerous bugs that resulted from some library returning an unexpected null, and the type system decided that was totally fine.
- josephlord 12y ago
  Yes C/C++ are pretty weakly typed and Null pointers are an issue in them all. They still catch some issues though and I find it does help me sometimes compared with Ruby for example. If they only caught 2% of the issues I would be a little surprised but it is certainly in the range of possibilities depending on the stage of development (I think it would catch more as you type your code but possibly 2% or less when evaluating a finished, debugged tested product). You can also add Swift to the list of languages that get it right in this regard. When receiving a return value from obj-c that can be null it comes back as an optional so you SHOULD safely transform it to a real value or only perform conditional actions on it. Of course there is the possibility to coerce it into the full type.

actsasbuffoon 12y ago

The interesting thing is that the majority of statically-typed languages wouldn't catch the null for you. C, C++, Java, C#, and many others accept null as a valid input for any type. There are plenty of languages like Haskell, Haxe, Idris, Agda, Roy, Rust, and Elm that get this right. Anecdotally it seems that most developers who advocate static typing aren't using these languages. It seems like the majority are writing in one of the Algol derived languages from the first paragraph. Scala gets it half right with Option, but included null for Java compat. I've not written much Scala, but I've already encountered numerous bugs that resulted from some library returning an unexpected null, and the type system decided that was totally fine.

josephlord 12y ago
Yes C/C++ are pretty weakly typed and Null pointers are an issue in them all. They still catch some issues though and I find it does help me sometimes compared with Ruby for example. If they only caught 2% of the issues I would be a little surprised but it is certainly in the range of possibilities depending on the stage of development (I think it would catch more as you type your code but possibly 2% or less when evaluating a finished, debugged tested product). You can also add Swift to the list of languages that get it right in this regard. When receiving a return value from obj-c that can be null it comes back as an optional so you SHOULD safely transform it to a real value or only perform conditional actions on it. Of course there is the possibility to coerce it into the full type.