単純な定義の代わりにマクロを使用しているBoost.Preprocessorの根拠？

Question

GMARのAnsSere ここのは、パラメータなしでプリプロセッサマクロです。BOOST_PP_ITERATEがないように単純な定義と使用されているだけでなく使用されている理由はありますか？

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.