G'day all.
Quoting Jerzy Karczmarczuk
Question of perspective... In Pascal, Modula, Python, Clean, you name it, modules and files were always 1 - 1.
A C++ class is basically an instantiable module. In C++, you can implement more than one module in a file, and you can implement a single module in multiple files.
Somehow this is considered more 'clean', isn't it?
It's usually considered good design practice in languages with modules to have one module responsible for one thing. Sometimes this is not possible, for example, if a module is responsible for implementing a major internal abstraction (e.g. "Core" in GHC, "database" in a database server etc). In that situation, it makes sense to distribute implementation of a module across more than one file. In Haskell, of course, you can do this by re-exporting symbols from imported modules; the Prelude is a case in point. Similarly, if a module is considered "private", such as with nested modules (or nested classes in C++), it is arguably cleaner to implement them privately lest someone else import them and use them. This usually means within the module which uses it, i.e., more than one module per file.
What's the problem with editing and displaying multiple files?
This reminds me of a previous discussion of tab stops for some reason. I feel like saying "here's a nickel, kid... buy yourself a decent text editor", but that's a bit rude. More nicely: It's not the programming language's job to take up the slack where your specific text editor is lagging, especially when I can name about half a dozen editors off the top of my head which can handle multiple files perfectly well.
I believe that our 21st century should finally forsake the old concept of file, as we see it now. A module is an entry in a database.
Be careful, lest you end up with a multiple maintenance problem. The reason why text files haven't gone the way of punched cards yet is that they're uniform and simple, and they're easy from a management point of view (one text file is one work assignment to a programmer in a team).
We have already separate 'interface files'...
...which are automatically generated. Cheers, Andrew Bromage