Finding the best match using metaprogramming technique

Question

I am investigating the best match algorithm whitch is represented in Template, the Complete Guide The implementation is the following

template<typename List>
class FrontT;

template<typename Head, typename... Tail>
class FrontT<Typelist<Head, Tail...>>
{
 public:
  using Type = Head;
};

template<typename List>
using Front = typename FrontT<List>::Type;
 template<typename List>
class PopFrontT;

template<typename Head, typename... Tail>
class PopFrontT<Typelist<Head, Tail...>> {
 public:
  using Type = Typelist<Tail...>;
};

template<typename List>
using PopFront = typename PopFrontT<List>::Type;
template<typename List>
class LargestTypeT;

// recursive case:
template<typename List>
class LargestTypeT
{
 private:
  using First = Front<List>;
  using Rest = typename LargestTypeT<PopFront<List>>::Type;
 public:
  using Type = IfThenElse<(sizeof(First) >= sizeof(Rest)), First, Rest>;
};

// basis case:
template<>
class LargestTypeT<Typelist<>>
{
 public:
  using Type = char;
};

template<typename List>
using LargestType = typename LargestTypeT<List>::Type;

That I hard understand is the following line

using Type = IfThenElse<(sizeof(First) >= sizeof(Rest)), First, Rest>;

It is clear that the First is the First Element in TypeList and sizeof it is the size of this type. But I confused with the Rest. What is the size of Rest? The Rest it is a list with the rest of the elements that are included in typelist.

For example, if the following is defined

LargestType<TypeList<int,bool,char>>

In the first loop First is int and sizeof is 4 Rest is bool,char , what is the sizeof ? In the second loop First is bool and sizeof is 1 Rest is char and sizeof is 1

Answer 1

What is the size of Rest? The Rest it is a list with the rest of the elements that are included in typelist.

No, Rest (which is a bit poorly named) is actually not the rest of the list, but rather the largest type in the rest of the list, as you can see from its definition:

using Rest = typename LargestTypeT<PopFront<List>>::Type;