Re: sunday afternoon whishlist

["Juris Kalnins" <juris@...>]

On Mon, 10 May 2010 19:51:05 +0300, HyperHacker <hyperhacker@gmail.com>  
wrote:

> An obvious one I see is what happens when you do this?
> t = {}
> t[1,2] = 42
> t[1,2] = 27
> On line 2 it's going to pass two parameters to __index, but on line
> three, unless a __usedindex or some such method is added (which I
> highly support and have already patched into my own copy), where do
> the multiple parameters go?

No, on line 2 it will error out, because there is no metatable, and
the default newindex(t, 1, 2, 42) would forward to newindex(t[1], 2, 42).
Same for the line three. If there _was_ a metatable for t, it's
__newindex would get called with all the parameters

On Mon, 10 May 2010 10:13:43 +0300, Eike Decker <zet23t@googlemail.com>  
wrote:

> Hm. Difficult.  To the called metatable function, the input of x[y,z]
> = v would look pretty similar to x[y,z,v] = nil. And if you'd pass
> more arguments than expected by your index function, you'd get some
> pretty "interesting" results ... so more or less, your index function
> would be required to accept (...) arguments and then expect the last
> value as the value to be assigned.

Right. The proposed calling convention is pretty random. 'x[] = 5' would
delete element with index 5 if the method is not "multi-aware", etc.
(But anyway, not being able to cheaply check number of arguments
passed to the function is .. "not convenient". Something
like "#..." would be really good to have)

The big idea actually was to have a meta interface that supports
multiple keys and multiple values; for lookup, insertion and for iteration.
Especially for iteration. But it doesn't seem possible with the Lua calling
convention. But multiple keys, single value might be possible.