Imports and includes in header files - when is it okay?

Question

I've read that the rule is to not #import or #include anything in .h files. Is that really true, though?

Just today I've run into two separate occasions where I had to do it, one where I import a header file that contains a typedef enum because my method stubs use it as parameters and another where I have to import a header file to declare delegatation.

What's the actual rule for these types of situations? Is it sometimes okay to do so – and if not, how can I do it differently?

Answer 1

There's no hard rule, but sometimes you do have to do it. You will also need to do if you inherit from something or need the protocol declaration.

In general I would restate the rule as "use forward declarations of @class and @protocol whenever possible."

Answer 2

If you've read such a rule, that rule is wrong. You can include (and import, which is just a safer way of include) things into your header, if that's something required for the interface declaration. Otherwise save it for the implementation files.

Answer 3

If ClassA depends on ClassB such that a consumer of ClassA is certainly going to need to import ClassB in order to make use of ClassA, I would prefer header imports over forward declarations.