Is it safe to unpack { nil, a, b } ?

[Niccolo Medici <niccolomedici@...>]

Officially, it's not correct to do "table.unpack{nil, 'something',
'another'}" because the nil makes it legitimate for table.unpack() to
regard the length of the table as 0.

However, all Lua implementations I've checked (Lua 5.1, 5.2, 5.3, JIT)
do calculate #{nil,a,b} to be 2, not 0. Let's assuming a and b are
never nil.

So I was wondering if this is a special case we can trust to always work.

<comment>

Why do I ask this?

Because sometimes I need to wrap one of the system functions. Such
functions return (nil, errmsg, errcode) on error. So I have the
following pattern in my code:

    local ret = { file:close() }
    -- do something
    return table.unpack(ret)

I know I can rewrite is as:

    local ret = table.pack( file:close() )
    -- do something
    return table.unpack(ret, 1, ret.n)

But sometimes I do "ret = { nil, a, b }" explicitly and it'd be
cumbersome to set the "n" field myself in all places.

</comment>