Typelists
A type list (also spelled typelist) is a compile-time construct that enables us to manage a sequence of types. A typelist is somehow similar to a tuple but does not store any data. A typelist only carries type information and is used exclusively at compile-time for implementing different metaprogramming algorithms, type switches, or design patterns such as Abstract Factory or Visitor.
Important Note
Although both the type list and typelist spellings are in use, most of the time you will find the term typelist in C++ books and articles. Therefore, this will be the form we will use in this book.
Typelists were popularized by Andrei Alexandrescu in his book, Modern C++ Design, published a decade before the release of C++11 (and variadic templates). Alexandrescu defined a typelist as follows:
template <class T, class U>
struct Typelist
{
typedef T Head;
typedef U Tail;
};
In his implementation, a typelist is composed of a head—...