Re: [Boost-users] [bind] [lambda] making lambda::bind work

From: Peter Barker (newbarker_at_[hidden])
Date: 2008-09-01 18:05:26

--- On Mon, 1/9/08, Peter Dimov <pdimov_at_[hidden]> wrote:

> From: Peter Dimov <pdimov_at_[hidden]>
> Subject: Re: [Boost-users] [bind] [lambda] making lambda::bind work
> To: boost-users_at_[hidden]
> Date: Monday, 1 September, 2008, 6:13 PM
> Peter Barker:
> 
> > void LambdaBind()
> > {
> > std::auto_ptr<GridItem> item(new GridItem());
> > std::vector<std::string> options;
> >
> > using namespace boost::lambda;
> > using boost::lambda::_1;
> > std::for_each(options.begin(),options.end(),
> > 
> >
> bind(GridItem::AddOption,boost::ref(item),bind(std::string::c_str,_1),true));
> > // COMPILE ERROR ON ABOVE
> > }
> >
> > int main()
> > {
> > }
> >
> > The error is:
> >
> c:\releases\lib\boost\boost_1_35_0\include\boost\bind.hpp(338)
> : error 
> > C2664: 'R
> boost::_mfi::mf2<R,T,A1,A2>::operator 
> > ()<std::auto_ptr<_Ty>>(const U
> &,A1,A2) const' : cannot convert parameter 
> > 2 from
> 'boost::lambda::lambda_functor<T>' to
> 'const char *'
> 
> Since you use an unqualified call to bind,
> argument-dependent lookup finds 
> boost::bind and prefers it as a better match. Nasty.

Thank you! It took me a while to figure out which argument made the compiler choose boost::bind. It was boost::ref(). After replacing that with var() I still had a compiler error as lambda::bind doesn't seem to work out of the box with std::auto_ptr. The following compiled:

void LambdaBind()
{
 GridItem item;
 std::vector<std::string> options;

 using namespace boost::lambda;
 using boost::lambda::_1;
 std::for_each(options.begin(),options.end(),
         bind(&GridItem::AddOption,var(item),bind(&std::string::c_str,_1),true));
 // NO COMPILE ERROR ON ABOVE :-)
}

> You need '&' in front of the member functions,
> by the way. Omitting it is a 
> MSVC-ism. 

Ahh - I'm glad to learn that. Many thanks for your help.
 
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