BOOST_CONTRACT_HEADER_ONLY — Automatically defined by this library when it is being used as a header-only library (not recommended).
// In header: <boost/contract/core/config.hpp> BOOST_CONTRACT_HEADER_ONLY
This macro is not a configuration macro and this library will generate a compile-time error if users try to define it directly. This library will automatically define this macro when users do not define
BOOST_CONTRACT_STATIC_LINK. When used as a header-only library, this library code does not have to be compiled separately from user code, this library headers are simply included and compiled as part of the user program.
This library is not guaranteed to always work correctly at run-time when this macro is defined (define