The BOOST_PP_ENUM macro generates a comma-separated list.
BOOST_PP_ENUM(count, macro, data)
The number of repetitious calls to macro.
Valid values range from 0 to BOOST_PP_LIMIT_REPEAT.
A ternary operation of the form macro(z, n, data).
This macro is expanded by BOOST_PP_ENUM with the next available repetition depth,
the current repetition number, and the auxiliary data argument.
Auxiliary data passed to macro.
This macro expands to the comma-separated sequence:
macro(z, 0, data), macro(z, 1, data), ... macro(z, count - 1, data)
The z value that is passed to macro represents the next available repetition dimension.
Other macros that have _Z suffix variants internally use BOOST_PP_REPEAT--for example, BOOST_PP_ENUM_PARAMS and BOOST_PP_ENUM_PARAMS_Z.
Using these _Z versions is not strictly necessary, but passing the z value (that is passed to macro) to these macros allows them to reenter BOOST_PP_REPEAT with maximum efficiency.
To directly use this z value, rather than simply passing it to another macro, see BOOST_PP_ENUM_z.
Previously, this macro could not be used recursively inside BOOST_PP_REPEAT.
This limitation no longer exists, as the library can automatically detect the next available repetition depth.