[Boost-users] Re: [MPL] How to Derive from inherit_linearly generated class?

Rick Sloan writes:

Hello all,

Given a mpl::list typedef mpl::list typeList; and a wrapper struct template <class T> struct wrap { virtual void someFunction(T&) = 0; virtual ~wrap }

You can generate a class by mpl::inherit_linearly,_1> >:;type generated;

This is pretty much straight from "C++ Template Metaprogramming" pg. 193-194.

My question is how do you generate the derived concrete class? I can override any particular function by

struct Child : public generated { virtual void someFunction(structA&); }

but I can't seem to generate an entire class.

1) Unless there is a specific reason to prefer "mixing in" 'wrap<T>' nodes (i.e. building 'inherit< wrap<T1>,inherit< wrap<T2>,... inherit ...> >') to "chaining" them into a linear hierarchy ('wrap ...> >'), I'd recommend going with the latter: struct base { virtual base() {} virtual void someFunction(T&) {} }; template struct wrap : Base { using Base::someFunction; // bring in Base overloads virtual void someFunction(T&) = 0; }; typedef mpl::inherit_linearly< types , wrap<_2,_1> , base >::type wrap_interface; 2) If I understood you question correctly, here's one way to generate a matching implementation for 'wrap_interface': template struct wrap_impl : Base { virtual void someFunction(T& x) { some_function_impl(x); } }; typedef mpl::inherit_linearly< types , wrap_impl<_2,_1> , wrap_interface >::type wrap_impl; void some_function_impl(T1& x ) { /* actual implementation for T1 */ } void some_function_impl(T2& x ) { /* actual implementation for T2 */ } ... HTH, -- Aleksey Gurtovoy MetaCommunications Engineering