These do not seem to be pure "header-only", but involve #include-ing the same file at least once with "#define C2_xxx_IMPLEMENTATION 1" That's fine though. AFA

These do not seem to be pure "header-only", but involve #include-ing the same file at least once with "#define C2_xxx_IMPLEMENTATION 1" That's fine though. AFAIK, there is no sane way (across platforms) to have singletons, and that involves some of the the trick above, unless you know someother way If you do, please add your idea here - https://github.com/open-telemetry/opentelemetry-cpp/issues/2534 https://github.com/open-telemetry/opentelemetry-cpp/issues/2... - "Header only singletons are not working properly for Windows #2534"