The BOOST_PP_LIST_FOLD_RIGHT macro folds (or accumulates) the elements of a list right-to-left.

Usage

BOOST_PP_LIST_FOLD_RIGHT(op, state, list)

Arguments

op
A ternary operation of the form op(d, state, elem).  This macro is called for each element in list--each time returning a new state.  This operation is expanded by BOOST_PP_LIST_FOLD_RIGHT with the next available BOOST_PP_WHILE iteration, the current state, and the current element.
state
The initial state of the fold.
list
The list to be folded.

Remarks

This macro does not have the same signature as it previously did.  The arguments have been swapped to provide a uniform interface with BOOST_PP_LIST_FOLD_LEFT.
For the list, (0, (1, (2, BOOST_PP_NIL))), this macro expands to:
op(d, op(d, op(d, state, 2), 1), 0)
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_FOLD_RIGHT_d in such a situation.

See Also

Requirements

Header:  <boost/preprocessor/list/fold_right.hpp>

Sample Code

#include <boost/preprocessor/cat.hpp>
#include <boost/preprocessor/list/fold_right.hpp>

#define LIST (a, (b, (c, BOOST_PP_NIL)))

#define OP(d, state, x) BOOST_PP_CAT(state, x)

BOOST_PP_LIST_FOLD_RIGHT(OP, _, LIST) // expands to _cba
© Copyright Housemarque Oy 2002
© Copyright Paul Mensonides 2002

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at www.boost.org/LICENSE_1_0.txt)