Re: Documentation for multiple assignment fails to mention order

[Niccolo Medici <niccolomedici@...>]

On 7/25/16, Roberto Ierusalimschy <roberto@inf.puc-rio.br> wrote:
>> > > <snip>
>> > > BTW, is it guaranteed that the assignment order goes from RIGHT to
>> > > LEFT (I verified this in Lua 5.1, 5.2, 5.3, LuaJIT), or is it
>> > > "undefined behavior"?
>> >
>> > It is not undefined behavior at all.
>> > <snip>
>> > It is like in C, which does not specify the order of evaluation of
>> > expressions in argument lists in function calls.
>>
>> You actually prove my point here. The C standard *does* say that the
>> order is "unspecified". [...]
>
> Check your words. "unspecified behavior" (what the C standard says) is
> different from "undefined behavior" (what you asked about). Lhf is
> correct in saying that the behavior is not undefined, even though it is
> unspecified.
>
> About the manual itself: there are infinite things that Lua does not do
> but the manual fails to mention. So, if the manual does not define in
> what order __newindex metamethods in multiple assignments are called,
> it is safe to assume that the order is unspecified, even if the manual
> does not say that.
>
> -- Roberto

Thank you for your reply.

I'll be going now to study the difference between "not undefined" to
"undefined" to "unspecified". I accept your judgment fully, so the
story is closed.

I did notice LHF's use of the phrase "not undefined" instead of
"unspecified", but I had to keep my post short so I removed that
section in my reply (which is fortunate because otherwise Dirk would
have had a stroke, not just a shock. I hope you didn't find me to be a
troll, or "not humble" as someone else said. I apologize if it perhaps
seemed this way. If it indeed seemed so, please let me know; I promise
not to reply - I'll just take it in mind seriously and try to learn
something from it).