The BOOST_PP_LIST_FILTER_D macro filters a list according to a supplied criterion.
It reenters BOOST_PP_WHILE with maximum efficiency.
Usage
BOOST_PP_LIST_FILTER_D(d, pred, data, list)
Arguments
- d
-
The next available BOOST_PP_WHILE iteration.
- pred
-
A ternary predicate of the form pred(d, data, elem).
This predicate is expanded by BOOST_PP_LIST_FILTER for each element in list with the next available BOOST_PP_WHILE iteration,
the auxiliary data, and the current element in list.
This macro must return a integral value in the range of 0 to BOOST_PP_LIMIT_MAG.
If this predicate expands to non-zero for a certain element, that element is included in the resulting list.
- data
-
Auxiliary data passed to pred.
- list
-
The list to be filtered.
Remarks
This macro expands pred for each element in list.
It builds a new list out of each element for which pred returns non-zero.
See Also
Requirements
Sample Code
#include <boost/preprocessor/comparison/less_equal.hpp>
#include <boost/preprocessor/list/filter.hpp>
#include <boost/preprocessor/list/fold_right.hpp>
#define A (1, (2, (3, (4, BOOST_PP_NIL))))
#define B (A, (A, (A, (A, BOOST_PP_NIL))))
#define PRED(d, data, x) BOOST_PP_LESS_EQUAL(x, data)
#define OP(d, state, x) (BOOST_PP_LIST_FILTER_D(d, PRED, 2, x), state)
BOOST_PP_LIST_FOLD_RIGHT(OP, BOOST_PP_NIL, B)
/*
expands to:
((1, (2, BOOST_PP_NIL)),
((1, (2, BOOST_PP_NIL)),
((1, (2, BOOST_PP_NIL)),
((1, (2, BOOST_PP_NIL)),
BOOST_PP_NIL))))
*/