06.09.2023 13:24, Yura Sokolov wrote:
24.08.2023 17:07, Maxim Orlov wrote:
Hi!
Recently, I've been playing around with pg_lists and realize how
annoying (maybe, I was a bit tired) some stuff related to the lists.
For an example, see this code
List *l1 = list_make4(1, 2, 3, 4),
*l2 = list_make4(5, 6, 7, 8),
*l3 = list_make4(9, 0, 1, 2);
ListCell *lc1, *lc2, *lc3;
forthree(lc1, l1, lc2, l2, lc3, l3) {
...
}
list_free(l1);
list_free(l2);
list_free(l3);
There are several questions:
1) Why do I need to specify the number of elements in the list in the
function name?
Compiler already knew how much arguments do I use.
2) Why I have to call free for every list? I don't know how to call it
right, for now I call it vectorization.
Why not to use simple wrapper to "vectorize" function args?
So, my proposal is:
1) Add a simple macro to "vectorize" functions.
2) Use this macro to "vectorize" list_free and list_free_deep functions.
3) Use this macro to "vectorize" bms_free function.
4) "Vectorize" list_makeN functions.
For this V1 version, I do not remove all list_makeN calls in order to
reduce diff, but I'll address
this in future, if it will be needed.
In my view, one thing still waiting to be improved if foreach loop. It
is not very handy to have a bunch of
similar calls foreach, forboth, forthree and etc. It will be ideal to
have single foreach interface, but I don't know how
to do it without overall interface of the loop.
Any opinions are very welcome!
Given use case doesn't assume "zero" arguments, it is possible to
implement "lists_free" with just macro expansion (following code is not
checked, but close to valid):
#define VA_FOR_EACH(invoke, join, ...) \
CppConcat(VA_FOR_EACH_, VA_ARGS_NARGS(__VA_ARGS__))( \
invoke, join, __VA_ARGS__)
#define VA_FOR_EACH_1(invoke, join, a1) \
invoke(a1)
#define VA_FOR_EACH_2(invoke, join, a1, a2) \
invoke(a1) join() invoke(a2)
#define VA_FOR_EACH_3(invoke, join, a1, a2, a3) \
invoke(a1) join() invoke(a2) join() invoke(a3)
... up to 63 args
#define VA_SEMICOLON() ;
#define lists_free(...) \
VA_FOR_EACH(list_free, VA_SEMICOLON, __VA_ARGS__)
#define lists_free_deep(...) \
VA_FOR_EACH(list_free_deep, VA_SEMICOLON, __VA_ARGS__)
There could be couple of issues with msvc, but they are solvable.
Given we could use C99 compound literals, list contruction could be
implemented without C vaarg functions as well
List *
list_make_impl(NodeTag t, int n, ListCell *datums)
{
List *list = new_list(t, n);
memcpy(list->elements, datums, sizeof(ListCell)*n);
return list;
}
#define VA_COMMA() ,
#define list_make__m(Tag, type, ...) \
list_make_impl(Tag, VA_ARGS_NARGS(__VA_ARGS__), \
((ListCell[]){ \
VA_FOR_EACH(list_make_##type##_cell, VA_COMMA, __VA_ARGS__) \
}))
#define list_make(...) list_make__m(T_List, ptr, __VA_ARGS__)
#define list_make_int(...) list_make__m(T_IntList, int, __VA_ARGS__)
#define list_make_oid(...) list_make__m(T_OidList, oid, __VA_ARGS__)
#define list_make_xid(...) list_make__m(T_XidList, xid, __VA_ARGS__)
(code is not checked)
If zero arguments (no arguments) should be supported, it is tricky
because of mvsc, but solvable.
