Multiple results and exact argument packs

The idea

Lua functions can return several values, but expression position controls how many are retained. A function call at the end of an expression list can contribute all its results; a call in an earlier position is adjusted to one result. Parentheses around a call also force a single result. These rules matter when forwarding helper results or building table constructors.

Varargs represent an argument list that may include nil values. A plain sequence table cannot reliably encode trailing nil arguments through its length operator. In Lua 5.4, table.pack stores an explicit n count, and table.unpack with bounds one through n can reconstruct the original arity. Distinguish the number of arguments from the number of non-nil values when designing wrappers.

local packed=table.pack(2,nil,7)
print(packed.n)
print(packed[2]==nil)
print(select("#",table.unpack(packed,1,packed.n)))

3
true
3

The explicit count retains arity even though the middle position is nil. Bounded unpack forwards all three positions.