Re: [boost] mistaken uses of <iostream>

From: Hervé Brönnimann (hervebronnimann_at_[hidden])
Date: 2006-11-20 22:23:45

On Nov 20, 2006, at 7:48 AM, John Maddock wrote:
> I think the problem here is that it's tricky to ensure that you  
> have all the
> necessary headers included: different implementations may or may  
> not flag up
> an error depending which headers you've included, so including  
> <iostream> is
> a sort of "belt-and-braces" approach.

The local fix for this is to write a library's cpp file that get  
compiled into the library.h, whose first line is #include  
"filename.h".  This ensures that all the right headers get pulled in  
properly.  In fact, the standard practice is to always include the  
headers in *reverse* order of dependency. The same works for the test  
driver: there is one test file dedicated simply to make sure that  
#include "filename.h" works without including anything else.  It's a  
bit of a discipline and one must make sure that all code template has  
been instantiated, so it (like anything else) is not foolproof.  You  
also need a notion of physical dependency and hierarchy levels. For  
this, I refer to John Lakos' book (whose second edition is in the  
writing).

> As an aside, I've always wanted a sort of "conceptual" std lib
> implementation, that included in each header nothing except what  
> absolutely
> has to be there.  Just the declarations would do, so we could do
> compile-time tests against it to verify inclusion of the right  
> headers: the
> only tricky bit is getting the compile time constants correct so  
> that it can
> still compile meta code.  Any volunteers? :->

John: I'm not sure I understand the only tricky bit.  Can you pls  
elaborate?
--
Hervé Brönnimann
hervebronnimann_at_[hidden]