Re: Lua strings as "atoms"???

[Rici Lake <lua@...>]

On 16-May-05, at 11:00 PM, Chris Marrin wrote:

> 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:

There was a discussion about this on the mailing list a while back, and 
the definitive answer from a Lua author was that when it says "the 
stack", it really means "the stack". That surprised me, too, but the 
manual is quite clear.

If the string is stored in the registry, it won't be garbage collected. 
But there is no *official guarantee* that it won't move. There is an 
*official guarantee* that it won't move if it is on the stack.

In practice, however, the standard implementation of Lua doesn't use a 
moving garbage collector, so the code you present is not going to fail 
with the current Lua version, as far as I know.

Whether that particular bit of code is faster than doing a pushstring 
or not, I don't know. I rather suspect it would be faster, at least for 
long strings. However, if you can use upvalues, you will find them to 
be faster than registry stashing -- although I rather sadly suspect 
that upvalues may not survive through the next n versions of Lua for 
some smallish value of n.

R.