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Having read through the thread so far I can definitely see the advantage for some situations for the existence of some kind of assignment-equivalent statement that supports multiple parameters, but I'm also convinced that extending [] is the wrong approach, for reasons including:

*Incompatibility without massive ugliness with the existing __newindex syntax *Potential breakage of existing code: function x() return 1,2; end some_object[x()] = 3;

Ideally there could be a new multi-arg indexing syntax with its own pair of metamethods, allowing for both multiple arguments **AND** multiple assignments?

Something like:

__setmulti(object, numIndices, ...)

Where matrix[1, 2] = 8.1, 0.0, 7.2;


_setmulti(matrix, 2, 1, 2, 8.1, 0.0, 7.2)

What I dont know (since I've not played with any of them) is whether any of the existing language extension mechanisms provides the framework required for this without modifying the language directly.


Chris wrote:
On Feb 19, 2008 5:59 PM, Daniel Stephens <> wrote:
Why does foo need to be a table at all in this example? Why not make it
a object with multi-arg get and set methods?

You're already signing yourself up for a function to implement the
functionality, trying to hide it behind lua syntax doesn't seem like a
particularly big win, though perhaps I'm missing something clever?

foo isn't a table, it's a userdata vector type.  My example was
probably a bad one too because I'm not attempting multiple depth
indexing.  A more realistic example would be:

vertex_vector[20, 'x'] = 2.5

My issue is sort of along the same lines as another thread here
recently talking about high performance math.  The problem is I want
to use the indexing syntax for readability but at the same time
prevent creation of millions of temporary objects.

Get/set functions do certainly work but since there will be lots of
different types of these vectors and this is one of the primary
interfaces my application uses the code would look horrible and be
difficult to manage.   I mean technically metamethods aren't needed at
all but we use them to make the interface better.  I'm just trying to
make the interface better if it would be a relatively simple patch to
the parser.

I'm open to ideas of better ways of handling this.  Currently I _am_
using get/set methods but it's really painful.