Re: Lua strings as "atoms"???

[Chris Marrin <chris@...>]

Rici Lake wrote:

> On 16-May-05, at 10:37 PM, Chris Marrin wrote:
>
> > ...
> > The other question is still outstanding, though. If I give a string to 
> > Lua, will it always give me back the same address in every call to 
> > lua_tostring() for that same sequence of characters? Does this work 
> > across GC cycles, for instance?
>
>
> The short answer is yes, providing the string doesn't get garbage 
> collected (that is, as long as you keep a reference to it somewhere).
>
> The longer answer is that the reference manual clearly states that the 
> string's address will remain constant provided the string is on the 
> stack. This presumably gives flexibility to language designers, but the 
> "reference implementation" of Lua does not currently take advantage of 
> that.

Ok, RTFM makes it a bit more clear. When it says "stack" it really means 
as long as the string exists as a valid object inside the Lua VM, right. 
It implies this where it talks about the registry (3.18). So that means 
I should be able to do this:

    lua_pushstring(L, "foo");
    const char * myFoo = lua_tostring(L, -1);
    lua_pushlightuserdata(L, s);
    lua_insert(L, -2);
    lua_rawset(L, L_REGISTRYINDEX);

Now I can put 's' in some global place and my C++ code can use this to 
do equality comparisons against strings in the stack, right? That would 
be very cool since I use strings a lot. If this is all true, then I can 
also push a string onto the stack like this:

    lua_pushlightuserdata(L, myFoo);
    lua_rawget(L, L_REGISTRYINDEX);

Any idea about whether this is faster that just calling 
lua_pushstring()? Has anyone tested the performance of this? If not, I 
can do it and let you know...

--
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