[webkit-dev] free functions

[Darin Adler]

On May 25, 2010, at 7:54 AM, Chris Jerdonek wrote:

> I sometimes come across public member functions whose implementations do not depend on private data.
> 
> There is a school of thought that such functions are better non-member because it reduces the number of functions coupled to private data. On the other hand, I've heard the argument that making such functions free creates naming issues -- it's not clear to the caller in which header file to find the free function.
> 
> My question for WebKit is whether naming considerations outweigh encapsulation considerations.  And if so, is there a naming convention or otherwise that we can use to make finding free functions easier?

We do need our classes to be smaller so we can understand the structure of the code. The encapsulation benefits of having a much smaller number of members in a class are well worth some cost. But there are at least two considerations that come into play when replacing a member function with a free function:

    1) Free functions still have to go in some header/source file. The usual rule for finding a function is to look for a file named based on the class. Without a class name we have to do something to make it practical to find the functions in the source tree without a lot of searching.

    2) Free functions need names that are clear and unambiguous with no context other than the WebCore namespace. We try to keep member function names short, and we can do so in part because they have a class name context. The same function as a free function will almost certainly need a longer name. Each time we create a free function we have to think about what an appropriate name is; it’s a mistake to leave the same short name that was previously used for a class member.

Another possible way to get encapsulation benefits with fewer of the other problems is to group functions into classes or namespaces that have no data and nothing else private. This may be helpful if the class or namespace name has a good name with a clear concept.

I also think that it’s fine for free functions to have longer names than member functions.

Functions like the ones in SuddenTermination.h, LinkHash.h, UUID.h, and even markup.h seem to be OK as free functions, so I think we can definitely deal with these issues and use them more. But it’s something I think we have to do carefully with sensitivity until we get a little more experience with it.

    -- Darin