Let's say we have a class called TypeCollection that holds a packed template of types:
template<typename ...Types>
class TypeCollection {};
And if we have a class that templates a TypeCollection you would need to do something a little like this:
template<template<typename ...> class Collection, typename ...Types>
class CollectionHandler {};
Which would be instantiated like so:
CollectionHandler<TypeCollecion, A, B, C>
This isn't great since we have to pass the types A B and C twice for template deduction. My question is if there is a way to do this without having to pass the types twice:
CollectionHandler<TypeCollecion<A, B, C>>
However I cant seem to get this to work. I tried a couple things and I realized that you cant pass a templated class as a parameter:
CollectionHandler<TypeCollecion<A, B, C>> // Error: Template argument for template template parameter must be a class template or type alias template
Is there a way to instantiate CollectionHandler without having to pass the types twice? I experimented with tuples to hide the parameters but I couldn't get that to work either.
Thanks for your help!
Flip your CollectionHandler declaration around to dissect the TypeCollection through template specialization:
template <class TypeCollection>
class CollectionHandler;
template <class... Types>
class CollectionHandler<TypeCollection<Types...>> { };