Best practices for reading public interfaces

[Kenny via Digitalmars-d-learn]

I like D modules and it's a major point in the list of major
points why I like D (there is also the second not so nice
wft-list but it's for another post). I'm annoyed with C++
includes and I'm tired to create 2 files every time when I need
to add something new to the project...  But I must admit that one
thing I like in header files is that it is a convenient way to
read public interfaces.

In D we have interface specification and implementation in a
single file and also one approach with unit testing is to put
them immediately after functions which makes writing unit tests
even more easy task (and I like it very much) but again it makes
the gaps between declarations even wider.

So, what are the common approaches for reading public interfaces
in D programs? Especially it would be great to see the answers of
developers who work with more or less big codebases.

The few possible solution I'm thinking about at the moment:

a) Provide D interfaces for corresponding classes (but probably
it's only for more or less complex abstractions and also I won't
use it for Vector3D, also very often I use just regular
functions).

b) Write DDocs and read documentation. The problem here is that
I'm going to use D only for my own projects and in the last time
I tend to write less documentation, for example I do not write it
for the most methods of Vector3D.

c) Do nothing special, just write D modules and try to figure out
public interfaces reading its code. Maybe it works in practice.

Thanks,
Artem.