[boost] Re: looping construct - testers wanted ;)

From: Eric Niebler (eric_at_[hidden])
Date: 2004-05-07 22:33:21

David Abrahams wrote:
> Maybe
> something could be done with "goto"?  I haven't looked at
> BOOST_FOREACH carefully, but I'm imagining something like:
> 
>     for (C::iterator s = c.begin(), f = c.end(); s != f; ++s) // outer
>     {
>         for(C::reference r = *s;;) // inner
>         {
>             // Body goes here
>             goto continue_;
>         }
>         break; // if there's a break in the body, break out all the way
>         continue_:
>     }

That won't work. Look how BOOST_FOREACH is used:

BOOST_FOREACH( int &i, int_vector )
{
     // body goes here
}

BOOST_FOREACH must expand to something such that the following scope is 
treated as the loop body. There is no place to put the continue_ label, 
and no place to put the goto. I thought about putting a goto somewhere 
in the inner for loop, like "for( ...; ; goto continue_ )" but C++ 
doesn't allow that. And even if that worked, it's still borken because a 
break in the loop body would skip the goto.

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com