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

Struct template eval

boost::proto::result_of::eval — A metafunction for calculating the return type of proto::eval() given a certain Expr and Context types.

Synopsis

// In header: <boost/proto/eval.hpp>

template<typename Expr, typename Context> 
struct eval {
  // types
  typedef typename Context::template eval< Expr >::result_type type;
};