The BOOST_PP_FOR macro represents a generalized horizontal repetition construct.
Usage
BOOST_PP_FOR(state, pred, op, macro)
Arguments
- state
-
The initial state.
- pred
-
A binary predicate of the form pred(r, state).
This macro must expand to an integer in the range of 0 to BOOST_PP_LIMIT_MAG.
BOOST_PP_FOR repeatedly expands macro while this predicate returns non-zero.
This macro is called with the next available BOOST_PP_FOR repetition and the current state.
- op
-
A binary operation of the form op(r, state).
This operation is expanded by BOOST_PP_FOR with the next available BOOST_PP_FOR repetition and the current state.
This macro is repeatedly applied to the state, each time producing a new state, until pred returns 0.
- macro
-
A binary macro of the form macro(r, state).
This macro is expanded by BOOST_PP_FOR with the next available BOOST_PP_FOR repetition and the current state.
This macro is is repeated by BOOST_PP_FOR until pred returns 0.
Remarks
This macro expands to the sequence:
macro(r, state) macro(r, op(r, state)) ... macro(r, op(r, ... op(r, state) ... ))
The r value that is passed to pred, op, and macro represents the next available BOOST_PP_FOR repetition.
Other macros that have _R suffix variants internally use BOOST_PP_FOR--for example, BOOST_PP_LIST_FOR_EACH and BOOST_PP_LIST_FOR_EACH_R.
Using these _R versions is not strictly necessary, but passing the r value (that is passed to pred, op, and macro) to these macros allows them to reenter BOOST_PP_FOR with maximum efficiency.
To directly use this r value, rather than simply passing it to another macro, see BOOST_PP_FOR_r.
Previously, this macro could not be used recursively inside BOOST_PP_FOR.
This limitation no longer exists, as the library can automatically detect the next available BOOST_PP_FOR repetition.
See Also
Requirements
Sample Code
#include <boost/preprocessor/arithmetic/inc.hpp>
#include <boost/preprocessor/comparison/not_equal.hpp>
#include <boost/preprocessor/repetition/for.hpp>
#include <boost/preprocessor/tuple/elem.hpp>
#define PRED(r, state) \
BOOST_PP_NOT_EQUAL( \
BOOST_PP_TUPLE_ELEM(2, 0, state), \
BOOST_PP_INC(BOOST_PP_TUPLE_ELEM(2, 1, state)) \
) \
/**/
#define OP(r, state) \
( \
BOOST_PP_INC(BOOST_PP_TUPLE_ELEM(2, 0, state)), \
BOOST_PP_TUPLE_ELEM(2, 1, state) \
) \
/**/
#define MACRO(r, state) BOOST_PP_TUPLE_ELEM(2, 0, state)
BOOST_PP_FOR((5, 10), PRED, OP, MACRO) // expands to 5 6 7 8 9 10