Re: [Boost-users] Delegating to boost::function with arbitrary signature

2013/12/14 Alexander Lamaison

I've asked this question on Stack Overflow but not found a solution yet: http://stackoverflow.com/q/20578575/67013. It's Boost.Function/MPL-related so I'll ask here too.

I'm trying to create something like a `boost::function`, but with an extra 'smart handle' tucked inside, which controls the lifetime of a resource the functions needs to execute correctly.

If I didn't need the function signature to be completely generic, this would be easy. I would just create a functor with the correct signature, and keep a `boost::function` and the handle as members.

However, I do need generic signatures. The code below is as close as I've got but gets a compile error, presumably, because I'm not able to unpack a list of arguments like this:

template<typename Signature> class library_function { public: library_function( library_handle handle, boost::function function) : m_handle(handle), m_function(function) {}

typename result_type operator()(arg1_type arg1, arg2_type arg2) { return m_function(arg1, arg2); }

// I don't think I can declare the 'params' like this ... typename boost::function_types::result_type<Signature>::type operator()( boost::function_types::parameter_types<Signature> params) { return m_function(params); // ... nor unpack them like this }

private: boost::function<Signature> m_function; library_handle m_library; };

I think `params` is an MPL list, so what I've actually done is declare a call operator with a single MPL-list parameter. My MPL-foo is not good. Is there a way to convert the list to a legal definition of multiple function paramters?

Why not just derive from boost::function so you get the call operator for free?