Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is an older version of Boost and was released in 2013. The current version is 1.89.0.

The MPL Reference Manual: Trivial Metafunctions Summary

Trivial Metafunctions Summary

In the following table, x is an arbitrary class type.

Metafunction	Header
`first<x>::type`	`#include <boost/mpl/pair.hpp>`
`second<x>::type`	`#include <boost/mpl/pair.hpp>`
`base<x>::type`	`#include <boost/mpl/base.hpp>`

See Also

Metafunctions, Trivial Metafunction