Re: lua_setfield vs lua_rawset

[Chris Marrin <chris@...>]

Rici Lake wrote:
> On 19-Oct-05, at 12:00 PM, Chris Marrin wrote:
>
> > But the decision was made to provide the particular variant of 
> > lua_setfield(), which is extremely useful. And since the "raw" 
> > variants add a useful (and sometimes critical) optimization of their 
> > own, it seems that the equivalent lua_rawsetfield() would have been a 
> > good choice.
>
>
> Have you actually benchmarked the difference in performance between 
> lua_settable() and lua_rawset()? It seems to me to be hardly noticeable 
> in the normal case. (That's not the same situation as lua_rawseti().)
>
> Using lua_rawset() instead of lua_settable() produces surprising results 
> (surprising to the client of the library, that is) because it doesn't 
> respect metatables. There is no difference when the table has no 
> metatable, or when the key already exists.
>
> I would strongly discourage use of rawset except in cases where it is 
> actually necessary because you have to bypass the __newindex metamethod. 
> Such cases are quite rare (usually confined to implementation of 
> __newindex itself).

Exactly where I am using it! I am actually using it in several places 
where I am setting the underlying table of my object system. This table 
is an internal detail of the implementation and I KNOW it does not have 
a metatable. I do notice a bit of performance gain when doing this, 
mostly when I write tests which repeatedly bang on this part of the code.

My concern in all this has been that lua_setfield() would be a big 
performance improvement on the pushstring(), replace(), settable() 
sequence that is required to do the equivalent operation. I was assuming 
that replace() is less optimal than the tricks that could be played 
internally to do the equivalant thing. But I've been doing some tests 
and, even when banging on it, the performance difference is negligible. 
I suppose this is because the replace() is always only having to move 
one item on the stack.

Anyway, once again Lua has proven to be so fast that optimizations 
aren't really needed!!!

--
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"As a general rule,don't solve puzzles that open portals to Hell"'