Boost.Preprocessor

#define BOOST_PP_LIST_FOLD_LEFT(OP,STATE,LIST)

Iterates OP(D,STATE,X) for each element X of the list LIST (from the left or the start of the list).

In other words, expands to:

OP
( D
, ... OP(D, OP(D,STATE,BOOST_PP_LIST_AT(LIST,0)), BOOST_PP_LIST_AT(LIST,1)) ...
, BOOST_PP_LIST_AT(LIST,BOOST_PP_DEC(BOOST_PP_LIST_SIZE(LIST))
)

For example,

#define TEST(D,STATE,X) BOOST_PP_CAT(STATE,X)
BOOST_PP_LIST_FOLD_LEFT(TEST,_,BOOST_PP_TUPLE_TO_LIST(3,(A,B,C)))

expands to:

_ABC

Note

• Folding, or accumulation, is a very general pattern of computation. Most list operations can be implemented in terms of folding.

See

• BOOST_PP_LIST_FOLD_RIGHT()

Test

• list_test.cpp

#define BOOST_PP_LIST_FOLD_LEFT_D(D,OP,STATE,LIST)

Can be used inside BOOST_PP_WHILE() (see for an explanation of the D parameter).

Note

• BOOST_PP_LIST_FOLD_LEFT_D() implements automatic recursion. You can use a fold in the OP macro.

#define BOOST_PP_LIST_FOLD_LEFT_2ND

Obsolete, just use BOOST_PP_LIST_FOLD_LEFT().

#define BOOST_PP_LIST_FOLD_LEFT_2ND_D

Obsolete, just use BOOST_PP_LIST_FOLD_LEFT_D().

Revised

© Copyright Housemarque Oy 2002

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