claude-skills/engineering/boost-asio-pro/references/classic-boost.md

Classic Boost (pre-1.66, the io_service era — verified to 1.62)

To support Boost older than 1.66 (no io_context, no make_strand, no any_io_executor), drop to the classic API — verified building back to Boost 1.62 (Debian 9) while still compiling on current Boost via a tiny shim:

Modern (1.66+)	Classic (pre-1.66)
io_context	io_service
make_strand(ex) / strand<any_io_executor>	io_service::strand strand(io)
bind_executor(strand, h)	strand.wrap(h)
timer.expires_after(d)	timer.expires_from_now(d)
move-return async_accept()	async_accept(socket_, handler)
header-only error_code	link Boost.System (find_package(Boost COMPONENTS system))

Only the io_service/io_context name and the expires_after/expires_from_now call actually differ across 1.62…1.90 — isolate both behind #if BOOST_VERSION >= 106600:

#include <boost/version.hpp>
#include <boost/asio/steady_timer.hpp>     // not pulled in by <boost/asio.hpp> on old Boost
#if BOOST_VERSION >= 106600
  using io_service_t = boost::asio::io_context;
#else
  using io_service_t = boost::asio::io_service;
#endif
template <class T, class Rep, class Period>
void timer_expires_in(T& t, std::chrono::duration<Rep,Period> d) {
#if BOOST_VERSION >= 106600
    t.expires_after(d);
#else
    t.expires_from_now(d);
#endif
}

CMake for this range: cmake_minimum_required(VERSION 3.5) (Debian 9 ships cmake 3.7), link Boost::system only if the component is found (modern Boost is header-only and has no such component), and use the classic out-of-source build (mkdir build && cd build && cmake ..) since -S/-B need cmake ≥ 3.13.