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Re: RFC: modules for generic unordered sets and mappings
From: |
Jim Meyering |
Subject: |
Re: RFC: modules for generic unordered sets and mappings |
Date: |
Sun, 04 Jul 2010 11:07:11 +0200 |
Jose E. Marchesi wrote:
> gl_set_search O(n) O(1)
>
> Here the search method returns a void *, with value (void*)-1
> denoting "not found". Hmm, or should the search method better
> take a 'bool *' argument???
>
> If 'gl_set_search' is merely testing the membership of an element in a
> set, would not suffice to make it to return a boolean value, like in:
>
> bool gl_set_search (void *key);
I think the goal of this function is to return the single (first?)
KEY-matching entry from the set, or some special value if there's no
match. However, that interface is subtly limiting, as Bruno appears to
have realized. I would prefer one like this:
bool gl_set_search (..., void const *key, void **match);
so as not to limit the range of valid "void*" result values.
Then we could even insert and query for a "NULL" key
or a key with that special value, (void*)-1.
I learned this the hard way, with hash_insert, since using NULL to
indicate "not found" precludes inserting "NULL" in hash.c. I added the
more general hash_insert0 method just a few days ago, but that removes
only the restriction that the inserted KEY be a pointer. There are
still some fundamental parts of hash.c that treat a NULL key as special.