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 1.90.0.

local::basic_endpoint::protocol_type

The protocol type associated with the endpoint.

typedef Protocol protocol_type;