"Michael Goldshteyn" <mgoldshteyn@earthlink.net> wrote in message news:d0l8qu$qfq$1@sea.gmane.org...

Given:

// Definitions

class Element { public: const std::string &GetTag() const; };

typedef std::vector<Element> ElementContainer;

// Now here is what is required

ElementContainer elements; ... ElementContainer matchingElements; std::string matchingTag("abc");

copy_if(elements.begin(),elements.end(),back_inserter(matchingElements)),pred);

--

What is pred? Assuming that iElements represents the iterator inside copy_if, pred should be something like: iElements->GetTag()==matchingTag

I could go about this by creating a new function object class/struct, which takes matchingTag as its sole constructor argument and does the comparison inside operator(). But, I want to use in place composition using binders, etc... to create the pred, so as not to have to create a function object class/struct. The question is, "What piece of code should pred be?"

// Almost does the right thing, but it's only *iElements==matchingTag, I need iElements->GetTag()==matchingTag bind_2nd(equal_to,matchingTag)

This seems like a very common operation. How can I compose the predicate, in place to do this? If there are multiple solutions, I would like to hear them as well!

Thanks,

Michael

The first way that comes to mind: copy_if( elements.begin() , elements.end() , back_inserter(matchingElements) , boost::bind<bool>( equal_to<string>() , boost::bind<string>( boost::mem_fn(&Element::GetTag) , _1 ) , matchingTag ) ); Note that I use the boost::bind<return_type> form, 'cuz I'm used to working with VC6 which can't deduce template arguments correctly. HTH Pablo Aguilar