Re: [Boost-users] [iterator || function_types] zip_iterator ->unpack and call?

shunsuke wrote:

Sohail Somani wrote:

...

Hi,

Say I have a function "int add(int, int)" and want to use it in a call to std::transform with zip_iterators. Is there a way to do it without writing an intermediate function object?

If not, would it be sensible to write a generic one using the function_types library? I can't imagine this would be too hard but just wanted to know if there is anything I can leverage before writing it myself.

I guess what you're looking for is...

http://tinyurl.com/26t9dd =http://lists.boost.org/Archives/boost/2007/01/115135.php

http://tinyurl.com/y9ax7t =http://boost.cvs.sourceforge.net/boost/boost/boost/iterator/zip_iterator.hpp?view=log&pathrev=zip_iterator_fusion

It seems not so easy because of the Forwarding Problem.

Forwarding doesn't seem a problem to me since you already have the argument tuple. The return type inference is painful to get right, though. On the surface it seems as easy as template ... unpack_and_call( F f, Tp const & tp ) { return unpack_and_call_( tuple_size<Tp>(), f, tp ); } template ... unpack_and_call_( mpl::int_<0>, F f, Tp const & tp ) { return f(); } template ... unpack_and_call_( mpl::int_<1>, F f, Tp const & tp ) { return f( get<0>(tp) ); } // and so on but the ... part is more involved if one decides to use result_of. boost::bind-style inference is of course easier since it only needs to look at F.