Re: [boost] version conflicts: is there a solution?

Subject: Re: [boost] version conflicts: is there a solution?
From: Ilya Bobir (ilya.bobir_at_[hidden])
Date: 2009-06-27 15:44:23

Frank Mori Hess wrote:
> On Thursday 25 June 2009, Edward Diener wrote:
>>> Can you point to anything in the standard that supports your position?
>> Where in the standard do you see any mention of an ODR violation
>> occuring where there are no header files being distributed for inclusion
>> by a source file which would create such a violation ?
> 
> There is the 3rd paragraph of the "one definition rule" section:
> 
> 
> "Every program shall contain exactly one definition of every non-inline 
> function or object that is used in that program; no diagnostic required. The 
> definition can appear explicitly in the program, it can be found in the 
> standard or a user-defined library, or (when appropriate) it is implicitly 
> defined (see 12.1, 12.4 and 12.8). An inline function shall be defined in 
> every translation unit in which it is used."
> 
> 
> Note they include "user-defined library".
> 

I think that in order to see the whole picture you need to explicitly 
define what a "definition" is.  ISO 14882-2003 3.1 paragraphs 1st and 2nd:

 > A declaration (clause 7) introduces names into a translation unit or
 > redeclares names introduced by previous declarations. A declaration
 > specifies the interpretation and attributes of these names.
 >
 > A declaration is a /definition/ unless it declares a function without
 > specifying the function’s body (8.4), it contains the extern specifier
 > (7.1.1) or a linkage-specification24) (7.5) and neither an initializer
 > nor a function-body, it declares a static data member in a class
 > declaration (9.4), it is a class name declaration (9.1), or it is a
 > typedef declaration (7.1.3), a using-declaration (7.3.3), or a
 > using-directive (7.3.4).

Unless your "user-defined library" include headers you can not introduce 
names into a translation unit.  And even if it does include headers the 
ODR applies only to the stuff you have in that headers and not to the 
"rest" of the library.  It means that unless you have the Boost headers 
somewhere in the header part of your library there is no way to violate 
the ODR as it applies to the translation units only.

The linkage of compiled translation units is described in a separate 
section and has its own rules.  Described in section "3.5 Program and 
linkage".  While there is something similar to ODR there, see paragraph 
9, but I do not think that it will apply to your case, unless you 
explicitly declare parts of boost as having external linkage thus making 
them visible to the linker during the linking process.