New subject: [lambda][bind] trivial bind fails when lambda and bind are in the same source file

20 Aug 2008

      My environment is VC9 SP1 and Boost 1.35. This problem also occurs in 
boost 1.36.

I had some code using lambda which worked fine for several weeks until 
today when someone else included my header in his code which used bind.

He told me my code was broken but my tests ran fine. It took us a few 
minutes to find the problem and I've distilled it to this trivial 
reproducible case.

#include <boost/bind.hpp>
#include <boost/lambda/bind.hpp>

void foo( int )
{

}

int main()
{
    using namespace boost::lambda;
    bind( &foo, _1 );
}

Compiling this gives:

error C2872: '_1' : ambiguous symbol
1>        could be 
'c:\vfx\third_party\boost\1_35_0\boost\lambda\core.hpp(69) : 
boost::lambda::placeholder1_type &boost::lambda::`anonymous-namespace'::_1'
1>        or 
'c:\vfx\third_party\boost\1_35_0\boost\bind\placeholders.hpp(42) : 
boost::arg<I> `anonymous-namespace'::_1'
1>        with
1>        [
1>            I=1
1>        ]

I can make the problem go away by changing main to

int main()
{
    using boost::lambda::_1;
    using boost::lambda::bind;
    bind( &foo, _1 );
}

but the actual code uses a lot more lambda and the amount of using 
directives I would need makes the code longer than rolling my own functor.

I could also alias lambda to make main look something like

int main()
{
    namespace bll = boost::lambda;
    bll::bind( &foo, bll::_1 );
}

but this introduces a lot of noise into the lambda expression and makes 
complex lambdas unreadable.

Is this accepted behavior?

Thanks,

Michael Marcin

[lambda][bind] trivial bind fails when lambda and bind are in the same source file

Michael Marcin

Peter Dimov

Markus Werle

Jeff Flinn

Markus Werle

Jeff Flinn

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