FreeTDS Development Group

[Frediano Ziglio <freddy77 AT gmail.com>]

Hi,
  as discussed recently adding a new type to libTDS is quite a nightmare!

I was thinking a different way to handle our types. Mainly something
similar to functions pointers we have but extended so support
everything. I would like to extend it in a way that every upper
library could have additional "methods" specific to this library.
However I want to not have to code of a specific library in libTDS.
libTDS should be able to get the table of a specific type with the
extended information and call method it needs. Only upper layer will
see additional methods. I'd like that when a new type is added to
libTDS compilation of upper layer will fail until type is correctly
supported. Also I'd like something that does not require many
allocation but I would prefer statically allocated structures. My
implementation idea is this:

libTDS has an array of pointer to structures indexed by type to the
function pointers, something like:

struct tds_type_pointers type_funcs[] = {
   ...
   funcs_chars,
   ...
   funcs_int,
};

Now, libTDS will provide implementations for functions but NOT for the
structures. That way to avoid link failures upper layers has to
provide the structures, better if they extend them. So for instance
ODBC could define an extended structure

struct odbc_type_pointers {
    tds_type_pointers common;
    unsigned (*get_sql_type)(TDSCOLUM *col);
};

...

struct odbc_type_pointers funcs_chars = {
    { tds_char_get, ...},
    odbc_get_char_sql_type;
}

Does we agree on doing that. Probably it will require some changes (a
lot) but adding a new type will be very easy! Probably will require
some additional macro and a lot of definitions but beside that we
avoid to miss some pieces.

Frediano