Re: [boost] ABI and API compatibility

From: Ravi (lists_ravi_at_[hidden])
Date: 2008-04-24 11:41:56

On Thursday 24 April 2008 08:06:12 am dizzy wrote:
> Actually directly using some class that changes implementation details
> (private members are added, modified, deleted) without recompilation of all
> involved parts leads to violation of ODR and thus UB.

If the size of the object changes, all ABI bets are off. If you use boost in a 
library (not an application) that you supply as headers + precompiled binary 
library, you must avoid using components from boost libraries (even if they 
are header-only) as:
  1. Members in your classes
  2. Direct arguments to member functions
If the size of a shared_ptr changed, the size of any class that contains a 
shared_ptr member also changes. Because of this issue, many libraries (such 
as those built on SystemC) include their own private (and usually incomplete) 
copy of boost. When using two such libraries in a project, all hell breaks 
loose when components in neither library but which could depend on common 
components in both libraries are used. Worse, when the libraries are header 
only, it is very easy to overlook this problem, especially since the 
compiler/linker does not provide any warnings.

I have been lucky enough that all issues have been fixable in the past couple 
of years, but eventually I will get a library vendor who uses boost, but will 
not provide source even under an NDA (or even worse, out of business), and 
then it will be a huge problem. It is already pretty hard to maintain 
internal forks of such libraries (even if the differences are only minor).

Regards,
Ravi