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Sean Conner wrote:
Here are some of the issues that need to be addressed for this to work.
1) t[a] = v This is syntactic sugar for t = { [a] = v }.  Then does that mean:
local t[a] = v is legal
Yes, local is legal.

2) t[a][b][c][d][e] = v -- when t[a][b] exists
An asusmption being made is that a,b,c,d,e are all tables.  They
don't have to be.  It could be a userdata that responds to both
__index and __newindex to act like a table.  Then this is fine, but
what if b*doesn't*  respond to __newindex?
a,b,c,d,e can be any valid table indices.  I assume you meant "what if t[a][b] doesn't respond to __newindex"?

Since t[a][b][c][d][e] = v is simply syntactic sugar, it should expand to the following, and will throw the same errors: (assuming in this case that the interpreter finds that t[a][b] already exists)

t[a][b][c] = {[d] = {[e] = v}}

If t[a][b] exists but doesn't respond like a table, an error will be thrown.

3) v = t[a][b][c][d][e]

	v ends up nil.  Which index is nil?
The nil return value will not provide this information.

4) Also, what about: t[a],t[b],t[c] = 1,2,3 How does this play out, syntactic surgar wise?
Although my proposal has more to do with multi-dimensional arrays, the same can be applied to new one-dimensional tables. If t is undefined, the above unambiguously means that t is intended to be a table, so following the principle that "When writing: automatically assign a single-entry table to each undefined variable, with the given index the sole entry", we get:
t = {[a] = 1}
t[b] = 2
t[c] = 3

4) t[a] [ t[B] ] [c][d][e] = v
If t doesn't exist, then what do we end up with?  If B doesn't
exist, what do we end up with?  It's hard to think about.
This should throw an "table index is nil" error, since t[B] is nil, and therefore an invalid index for assignment. N.B.:  My proposal is not that nil or NaN should become valid table indices, and my "syntactic sugar for autovivification" (if I may borrow the Perl term) will only apply when the indices are valid, and only when assigning, not when reading.

5) t[a][0/0][c][d][e] = v
The previous question brings this up---what if the index is NaN?
Rare, but possible.  Treat it as nil?  Error?
As in question (4), this should throw an error, since it is an assignment to an invalid index.

Currently, Lua throws an error when assigning to an invalid index (nil or NaN), but returns nil when reading from the same:
t[0/0] = 1 throws "table index is NaN" error,
v = t[NaN] just returns nil.