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

Subject: Re: [Boost-users] Delegating to boost::function with arbitrary signature
From: TONGARI J (tongari95_at_[hidden])
Date: 2013-12-14 10:20:38

2013/12/14 Alexander Lamaison <awl03_at_[hidden]>

> 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<result_type(arg1_type, arg2_type)> 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?