more typelists & templates

My co-worker Aaron was quick to reply to my earlier post on templates in type-lists with this alternative:

You instead add a non-templated function invoker object:

 

struct factory_invoker{

    template <class a, class b>

    struct apply{

        typedef typedef factory<a,b>::type type;

    };

};

 

Then your typelist has normal types in the list, but those types happen to be template metafunctions. To invoke one of these that is in a typelist:

 

// assuming tlist1 is a typelist

typename tlist1::head::template apply<int, char>::type

 

(the above ‘template’ and ‘typename’ keywords are, as always, only required or even allowd when used inside a template)

Which in this case will end up naming the type ‘MyType<int, char>’ for you.

This also works. However in my case since I was trying to reduce the number of generated types, so I stuck with the previous solution.

Thanks Aaron!

Comments

• Anonymous
  August 15, 2008
  Also note that the following definition of factory_invoker is also valid and more concise, provided that your factory returns types by the typedef 'type'   struct factory_invoker{       template <class a, class b>       struct apply : factory<a,b>{ };   };The typedef is only strictly necessary when adapting template metafunction return type names.#aaron