Can I write C++ code without headers (repetitive function declarations)?

Question

Is there any way to not have to write function declarations twice (headers) and still retain the same scalability in compiling, clarity in debugging, and flexibility in desi

Answer 1

This has been "revived" thanks to a duplicate...

In any case, the concept of a header is a worthy one, i.e. separate out the interface from the implementation detail. The header outlines how you use a class / method, and not how it does it.

The downside is the detail within headers and all the workarounds necessary. These are the main issues as I see them:

• dependency generation. When a header is modified, any source file that includes this header requires recompilation. The issue is of course working out which source files actually use it. When a "clean" build is performed it is often necessary to cache the information in some kind of dependency tree for later.

• include guards. Ok, we all know how to write these but in a perfect system it would not be necessary.

• private details. Within a class, you must put the private details into the header. Yes, the compiler needs to know the "size" of the class, but in a perfect system it would be able to bind this in a later phase. This leads to all kinds of workaround like pImpl and using abstract base classes even when you only have one implementation just because you want to hide a dependency.

The perfect system would work with

• separate class definition and declaration
• A clear bind between these two so the compiler would know where a class declaration and its definition are, and would know what the size of a class.
• You declare using class rather than pre-processor #include. The compiler knows where to find a class. Once you have done "using class" you can use that class name without qualifying it.

I'd be interested to know how D does it.

With regards to whether you can use C++ without headers, I would say no you need them for abstract base classes and standard library. Aside from that you could get by without them, although you probably would not want to.