Justificación en Boost.Preprocessor ¡Usando macros en lugar de define simple?

Question

Por ejemplo, BOOST_PP_ITERATE y BOOST_PP_ITERATION, como se ve en la respuesta de GMAN aquí , son macros de preprocesadores, sin parámetros.¿Hay alguna razón por la que no son simplemente simples define y se usan como tales sin ()?

Answer 1

Generally, function like macro can be used to prevent unintentional macro expansion.
For example, assuming that we have the following macro call:

BOOST_PP_CAT( BOOST_PP_ITERATION, _DEPTH )

and we expect this will be expanded into BOOST_PP_ITERATION_DEPTH.
However, if BOOST_PP_ITERATION is an object like(non-functional) macro, it will be expanded to its own definition before the token BOOST_PP_ITERATION_DEPTH is generated by concatenation.

Answer 2

Presumably because they perform operations: consequently, their usage should make it clear that you are actually invoking something and not just using some constant.