There are several configuration macros that control the behavior of the Fit library.

Name Description
FIT_CHECK_UNPACK_SEQUENCE Unpack has extra checks to ensure that the function will be invoked with the sequence. This extra check can help improve error reporting but it can slow down compilation. This is enabled by default.
FIT_NO_EXPRESSION_SFINAE This controls whether the Fit library will use expression SFINAE to detect the callability of functions. On MSVC, this is enabled by default, since it does not have full support for expression SFINAE.
FIT_RECURSIVE_CONSTEXPR_DEPTH Because C++ instantiates constexpr functions eagerly, recursion with constexpr functions can cause the compiler to reach its internal limits. The setting is used by Fit to set a limit on recursion depth to avoid infinite template instantiations. The default is 16, but increasing the limit can increase compile times.