Re: [boost] C++03 / C++11 compatibility question for compiled libraries

Subject: Re: [boost] C++03 / C++11 compatibility question for compiled libraries
From: Peter Dimov (lists_at_[hidden])
Date: 2018-02-08 14:20:18

Edward Diener wrote:

> As far as which library to use, depending on the compiler/version 
> available, either boost or std, of two very similar libraries, this is 
> what my Cxx_dual library (https://github.com/eldiener/cxx_dual) is all 
> about.

That's not going to work at all if link compatibility is desired. If you 
have

class something
{
private:

    CXXD::function<void()> f_;

public:

    // ...
};

the layout of `something` changes between C++03 and C++11, which leads to 
incredibly nasty things at runtime as objects appear at the wrong address 
and the observed behavior makes no sense.

I inadvertently introduced such a problem in Boost.System when I made the 
object layout dependent on whether <system_error> was available, to enable 
conversions from/to std::error_code. It's not fun at all. (I have since 
fixed that, and added tests that link to the library from a forced-03 or 
forced-11 main.cpp. Incidentally, the layout of std::string also changes 
between 03 and 11, so if such compatibility is desired, you can't use that 
either.)

(But there's absolutely no need to use std::function "for std::bind 
compatibility". boost::function can store std::bind just fine (and vice 
versa.))