The BOOST_PP_LIST_FOLD_LEFT_d macro folds (or accumulates) the elements of a list left-to-right.
It reenters BOOST_PP_WHILE with maximum efficiency.
Usage
BOOST_PP_LIST_FOLD_LEFT_ ## d(op, state, list)
Arguments
- d
-
The next available BOOST_PP_WHILE iteration.
- 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_LEFT 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
For the
list, (
0, (
1, (
2,
BOOST_PP_NIL))), this macro expands to:
op(d, op(d, op(d, state, 0), 1), 2)
See Also
Requirements
Sample Code
#include <boost/preprocessor/cat.hpp>
#include <boost/preprocessor/list/fold_left.hpp>
#define L1 (a, (b, (c, BOOST_PP_NIL)))
#define L2 (L1, (L1, (L1, BOOST_PP_NIL)))
#define OP(d, state, x) (BOOST_PP_LIST_FOLD_LEFT_ ## d(OP_2, _, x), state)
#define OP_2(d, state, x) BOOST_PP_CAT(state, x)
BOOST_PP_LIST_FOLD_LEFT(OP, BOOST_PP_NIL, L2)
/*
expands to:
(_abc, (_abc, (_abc, BOOST_PP_NIL)))
*/