Re: Possible enhancements for Lua 5.2

[Andre Leiradella <andre@...>]

On 25/06/2011 22:37, Wesley Smith wrote:
> > const char* lua_tohstring( lua_State *L, int index, unsigned int *hash );
> >
> > When writing bindings I usually get the key string in __index/__newindex
> > metamethods and compute some hash with them which then I use in a switch. It
> > would be nice if I could save the time spent in computing this hash since
> > Lua already has one.
>
> How could you use the hash in a switch statement if the hash result
> isn't a compile-time calculation?
> wes
I'd generate the hashes with a command-line tool ( lua_pushstring(...); 
lua_tohstring(...); ) and put them into the source code, just like I do now.

static int index( lua_State* L )
{
    unsigned int hash;
    const char* key = lua_tohstring( L, 1, &hash );

    if ( key == NULL )
    {
        return luaL_error( L, "key is not a string" );
    }

    switch ( hash )
    {
    case 0x12345678: /* pre-computed hash */
        ....
    case 0x87654321: /* pre-computed hash */
        ...
    }

    return luaL_error( L, "invalid key: %s", key );
}