RE: [Boost-Users] Struggling with bind

From: Jean-Marc Prud'homme (JPrudhomme_at_[hidden])
Date: 2003-06-10 11:01:37

Hi Paul,

_1 is a placeholder argument.  When you write 

bind(&CDocumentAttachments::Execute, _1, _T("print")) 

you are creating a functor that can be called with a single argument 
of type CDocumentAttachments.  This is what is required by the for_each 
algorithm. It is equivalent to

bind<HINSTANCE>(mem_fn(&CDocumentAttachments::Execute), _1, _T("print")) 

Look at the mem_fn doc.

You still need this kind of functor if you add more arguments to 
CDocumentAttachments::Execute.  This should create the functor you
need

bind(&CDocumentAttachments::Execute, _1, _T("print"), false) 

Hope this helps,

Jean-Marc

-----Original Message-----
From: Paul Thompson [mailto:friedegg_at_[hidden]]
Sent: Tuesday, June 10, 2003 7:54 AM
To: Boost-Users_at_[hidden]
Subject: [Boost-Users] Struggling with bind

Hi all.

I've been using boost::bind to work around deficiencies with
std::mem_fun_ref and std::bind2nd under MSVC6.

I have a class called CDocumentAttachments which had a member 
function thus:

    HINSTANCE Execute(LPCTSTR verb) const;

I was using bind with this as follows:

    for_each(filenames.begin(),
             filenames.end(),
             bind(&CDocumentAttachments::Execute, _1, _T("print")));

"filenames" is a const vector of CDocumentAttachments objects.

This worked fine.

A little later on in development, I changed the function signature for
CDocumentAttachments::Execute to:

    HINSTANCE Execute(LPCTSTR verb, bool visible) const;

How will I pass the extra bool to bind?  I can't find any examples of
passing more than one parameter to a member function.

I thought about (among many others)

    for_each(filenames.begin(),
             filenames.end(),
             bind(&CDocumentAttachments::Execute, _2, _T("print"), 
false));

but the compiler (VC6) complains with two of the following:

k:\vc\include\boost\bind.hpp(760) : error C2679: binary '[' : no 
operator
defined which takes a right-hand operand of type 'const class 
boost::arg<2>'
(or there is no acceptable conversion)
        k:\vc\include\boost\bind\bind_template.hpp(33) : see 
reference to
function template instantiation 'struct HINSTANCE__ *__cdecl
boost::_bi::evaluator3<struct HINSTANCE__ *>::eval(const class
boost::_bi::list3<class boost::arg<2>,class boost::
_bi::value<char *>,class boost::_bi::value<bool> > &,struct
boost::_mfi::cmf2<struct HINSTANCE__ *,class 
CDocumentAttachments,char const
*,bool>,class boost::_bi::list1<class CDocumentAttachments const &> 
&)'
being compiled

I know I'm being really thick here, and I'm sure there's something 
really
obvious that I'm missing, but reading through the documentation hasn't
helped me.

Thank you very much.

Paul

--
Paul Thompson
Programmer
McLellan Software Design Ltd.
Info: <http://www.boost.org>
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