#include <boost/phoenix/scope/local_variable.hpp>

We use an instance of:

expression::local_variable<Key>::type

to represent a local variable. The local variable acts as an imaginary data-bin where a local, stack based data will be placed. Key is an arbitrary type that is used to identify the local variable. Example:

struct size_key;
expression::local_variable<size_key>::type size;

Predefined Local Variables

There are a few predefined instances of expression::local_variable<Key>::type named _a.._z that you can already use. To make use of them, simply use the namespace boost::phoenix::local_names:

using namespace boost::phoenix::local_names;