Re: [boost] bug-sprint #2114, 2 comments

Subject: Re: [boost] bug-sprint #2114, 2 comments
From: Ilya Sokolov (ilyasokol_at_[hidden])
Date: 2009-06-11 03:50:54

Alexander Arhipenko wrote:
> [snip]
> I have written down 2 sample configuration files for the 'foo' library.
> 
> #if !defined BOOST_FOO_DETAIL_CONFIG_HPP
> #define BOOST_FOO_DETAIL_CONFIG_HPP
> 
> #if defined BOOST_FOO_BUILD_SHLIB

Should be named BOOST_FOO_SOURCE.

> # define BOOST_FOO_DECL                       BOOST_SYMBOL_EXPORT
> # define BOOST_FOO_EXCEPTION_DECL   BOOST_EXCEPTION_EXPORT
> #elif defined BOOST_FOO_USE_SHLIB

Just #else should be enough, see the 'Supporting Windows Dll's' section 
at http://www.boost.org/development/separate_compilation.html

> # define BOOST_FOO_DECL                       BOOST_SYMBOL_IMPORT
> # define BOOST_FOO_EXCEPTION_DECL   BOOST_EXCEPTION_IMPORT
> #else
> # define BOOST_FOO_DECL
> # define BOOST_FOO_EXCEPTION_DECL
> #endif
> 
> #endif
> 
> Configuration file above will re-export all the exceptions marked with
> BOOST_FOO_EXCEPTION_DECL from shared library foo.
> So, if I write library 'bar', it will contain all the symbols exported by 'bar'
> and also all the exceptions from 'foo' library'.
> This is intended for the following scenario:
> 
> exe test : main.cpp bar ;
> 
> main.cpp:
> 
> #include <bar.hpp>
> #include <foo/error.hpp>
> 
> int main()
> {
>    try
>    {
>       bar::function();//could potentially throw foo's exception
>    }
>    catch(const foo::error& e)
>    {
>       std::cerr<<"error occured: "<<e.what()<<'\n';
>    }
> 
>    return 0;
> }
> 
> In case if 'bar' reexports exceptions from 'foo', the code above will succeed.
> Otherwise it will be aborted, since foo::error won't be caught.
> 
> But, all these could be not enough for the sophisticated user.
> Assume, library 'bar' will use library 'foo' as an implementation detail
> and also will catch all the foo's exceptions. So, bar's maintainer doesn't want
> to re-export foo's stuff from his library. As a result, foo's
> maintainer should provide
> more sophisticated configuration file (I marked changes with '+'):
> 
>  #if !defined BOOST_FOO_DETAIL_CONFIG_HPP
>  #define BOOST_FOO_DETAIL_CONFIG_HPP
> 
> #if defined BOOST_FOO_BUILD_SHLIB
> # define BOOST_FOO_DECL                       BOOST_SYMBOL_EXPORT
> # define BOOST_FOO_EXCEPTION_DECL   BOOST_EXCEPTION_EXPORT
> #elif defined BOOST_FOO_USE_SHLIB
> # define BOOST_FOO_DECL                       BOOST_SYMBOL_IMPORT
> +# if defined BOOST_FOO_EXCEPTION_REEXPORT

Exceptions should be re-exported by default, IMHO.

> #  define BOOST_FOO_EXCEPTION_DECL   BOOST_EXCEPTION_IMPORT
> +# else
> +#  define BOOST_FOO_EXCEPTION_DECL   BOOST_SYMBOL_IMPORT
> +# endif
> #else
> # define BOOST_FOO_DECL
> # define BOOST_FOO_EXCEPTION_DECL
> #endif
> 
> #endif
> 
> So, now bar library maintener have a choice:
> 1. Re-export foo's exceptions and let them left the bar library's boundaries
> 2. Catch all the foo's exceptions, process and do not re-export
> 
> P.S.
> I've attached minimal bbv2 project that reproduce the problem
> with uncaught exception. To eliminate it, you can do the following:
> a) Replace FOO_DECL with FOO_EXCEPTION_DECL in Error class declaration
> b) Uncomment ~Error() declaration (foo/error.hpp) and definition (foo/foo.cpp)
> 
> 
> ------------------------------------------------------------------------
> 
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