Re: [boost] [function] invoking without requiring boost::throw_exception

Subject: Re: [boost] [function] invoking without requiring boost::throw_exception
From: Domagoj Saric (dsaritz_at_[hidden])
Date: 2010-09-04 15:33:19

From: "Peter Myerscough-Jackopson" <peter.myerscough-jackopson_at_[hidden]>
Sent: Thursday, September 02, 2010 5:36 PM
> I am using boost::function on an embedded platform, which requires me to
> not use exceptions, and as commented in the thread associated with
>
> http://article.gmane.org/gmane.comp.lib.boost.devel/195351
>
> I am checking that the function object contains a function before
> calling it. There is therefore no need for the invocation of the
> function to check if it is valid, but also there is no method circumvent
> this checking, and therefore my program requires the definition of
> boost::throw_exception, when really it is not needed. This is a concern
> because I intend on compiling my code into a library and do not wish to
> require the user to define boost::throw_exception, especially when I am
> guaranteeing it isn't going to be called from this site. I liked the
> idea of a templated NOP for the function library, but at the very least
> an unchecked invocation method would be great, or a nop-if-empty
> invocation method would be useful.

If you are certain that neither you nor your users use or will use 
boost::throw_exception (to actually handle some other cases 'exceptional' 
cases in other parts of boost) then you can provide the definition yourself. 
Something along the lines of:
void throw_exception( std::exception const & )
{
    assert( !"Should not get reached." );
    #ifdef _MSC_VER
        __assume( false );
    #elif defined( __GNUC__ )
        __builtin_unreachable();
    #else
        ....
    #endif
}
should pretty much completely remove the if-then-throw code from your 
release binary...

ps. the code mentioned in the thread you linked to has since somewhat 
progressed and can always be found @ 
https://svn.boost.org/svn/boost/sandbox/function/boost/function ... but it 
is still in an unfinished-alpha-msvc specific stage ... I haven't touched it 
in months as there has not been any real response from the official 
maintainer and I've been swamped with other things (and am currently working 
on GIL::IO) but will surely finish it when I get the time (now that I've 
started working with GCC also)...

-- 
 "That men do not learn very much from the lessons of history is the most
important of all the lessons of history."
 Aldous Huxley