The BOOST_PP_LIST_FILTER macro filters a list according to a supplied criterion.
Usage
BOOST_PP_LIST_FILTER(pred, data, list)
Arguments
- 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.
Previously, this macro could not be used inside BOOST_PP_WHILE.
There is no longer any such restriction.
It is more efficient, however, to use BOOST_PP_LIST_FILTER_D in such a situation.
See Also
Requirements
Sample Code
#include <boost/preprocessor/comparison/less_equal.hpp>
#include <boost/preprocessor/list/filter.hpp>
#define LIST (1, (3, (2, (5, BOOST_PP_NIL))))
#define PRED(d, data, elem) BOOST_PP_LESS_EQUAL(elem, data)
BOOST_PP_LIST_FILTER(PRED, 3, LIST)
// expands to (1, (3, (2, BOOST_PP_NIL)))