2011/7/18 Edward Diener
On 7/17/2011 1:29 PM, Edward Diener wrote:
On 7/17/2011 9:21 AM, TONGARI wrote:
Hello,
I'd like to have a macro like:
BUILD_HIERARCHY (a, (b,) (c, (d,) (e,) ) )
which should expand to:
struct a {}; struct b: a {}; struct c: a {}; struct d: c {}; struct e: c {};
Is this possible at all? I have tried but with no luck, if this is impossible, please tell me so.
I think you want above:
(a, (b) (c, (d) (e) ) )
This is a tuple with a possible second element as a seq. Each element of your seq is a tuple with the same rule as the top tuple.
Following internal logic, perhaps with nested BOOST_PP_WHILEs, you should be able to cycle through each tuple and nested tuple forming the relationships you have created for your structs above. I can not guarantee this will be doable but at least you should have some idea of what to do from the description of what you have.
I have to correct the above. The syntax for what I described must be:
(a, ((b)) ((c, (d) (e)) )
)
I think I need the comma since I don't assume variadic macro. This is what I had (not working, of course): #define PACK_2A( a1, a2 ) ((a1, a2)) PACK_2B #define PACK_2B( a1, a2 ) ((a1, a2)) PACK_2A #define PACK_2A_END #define PACK_2B_END #define BUILD_SUB( x, parent, child ) \ struct BOOST_PP_TUPLE_ELEM(2, 0, child) : parent {};\ BOOST_PP_SEQ_FOR_EACH\ (\ BUILD_SUB, BOOST_PP_TUPLE_ELEM(2, 0, child)\ , BOOST_PP_CAT(BOOST_PP_EXPAND(PACK_2A BOOST_PP_TUPLE_ELEM(2, 1, child)), _END)\ ) #define BUILD_HIERARCHY( root, children ) \ struct root {};\ BOOST_PP_SEQ_FOR_EACH\ (\ BUILD_SUB, root\ , BOOST_PP_CAT(PACK_2A children, _END)\ ) Obviously BUILD_SUB cannot be that way since the preprocessor disallows recursion. But even if I replace the recursive BUILD_SUB with something else the BOOST_PP_SEQ_FOR_EACH inside BUILD_SUB still fails to expand. I have no ideas :/ Thanks for your time.