Re: Size of a non numerical indexed table

[Mark Hamburg <mhamburg@...>]

on 9/1/05 6:19 AM, Wim Couwenberg at wcou@oce.nl wrote:

> the ipairs generator will stop at the first nil.  To safely iterate over
> all arguments use:
> 
>    for i = 1, select("#", ...) do
> local a = select(i, ...)
>        -- etc...
>    end

This takes time that is quadratic in the number of elements though the
proportionality constant is probably low.

>    local arg = {...}
>    for i = 1, select("#", ...) do
> local a = arg[i]
>        -- etc...
>    end

This takes time linear in the number of elements but it has a higher
constant term and possibly proportionality factor to build the table.

I've been contemplating whether Lua needs:

    function argforeach( fn, ... )
        for I = 1, select( "#", ... ) do
            fn( ( select( I, ... ) ) )
        end
    end

This should be written in C to avoid the performance issues cited above and
probably needs a better name.

An alternative would be to extend the syntax to define:

    for i, v in ... Do
        -- do stuff with the i-th element of ...
    end

So that it implements the appropriate loop. This means that if you want to
pass iteration parameters via ..., then you will need to bind them to locals
outside of the loop or use select( 1, ... ) in the loop.

Mark

P.S. The absence of standard support for packing and unpacking argument
lists containing nil is an annoyance.