Re: ... efficiency (was Re: class implementation)

[Mike Pall <mikelu-0604@...>]

Hi,

Mark Hamburg wrote:
> 1. #... should be the same as select( '#', ... ) but should be able to avoid
> copying the values around.

This already has a syntactic meaning (not that it would be missed
much). But special casing #... lowers the language consistency.

> 2. ...[ j ] should be the same as ( select( j, ... ) ) but again bypassing
> the need to copy values around.

Well, if you are passing much more than a handful of values to a
vararg function, then you are better off with a table, anyway.
And if you are passing just a few, then why worry about
performance?

I mean how often do you ...
a. call a vararg function in the critical code path,
b. with lots of arguments (>30 or so),
c. and need to iterate over all of them one-by-one?

> Or at the very least, the Lua library needs a standard function to generate
> an iterator from a series of values so that one could write:
> 
>     for i, arg in varargs( ... ) do
>         -- code goes here
>     end

This one needs to allocate and GC a heap object _and_ copy the
values around. Copying a handful of values around (even
repeatedly) may or may not be more efficient.

> (It doesn't really need to be named "varargs" since one also ought to be
> able to write things like varargs( "red", "green", "blue" ). I just wasn't
> feeling creative about a name.)

apairs() -- argument pairs.

Would be useful even for non-vararg cases. I'd like to have this
as standard given that the implementation takes only a few lines
(but it would be limited to 255 elements or needs to defer to
table or coroutine storage).

Bye,
     Mike