Re: Returning nil vs returning nothing

[Andrew Gierth <andrew@...>]

>>>>> "Viacheslav" == Viacheslav Usov <via.usov@gmail.com> writes:

 >> The examples that use pack/unpack seem misguided since they're
 >> allocating a table unnecessarily.

 Viacheslav> Speaking of my example, it answered the two questions
 Viacheslav> above, not just the second one. PiL 3 recommends that
 Viacheslav> tables are the general way to handle variadic arguments.
 Viacheslav> There was a discussion and some benchmarking here four-five
 Viacheslav> years ago, when it was found that one should worry about
 Viacheslav> the impact of table creation only when the actual number of
 Viacheslav> variadic arguments is 0, 1 or 2. With progressively more
 Viacheslav> variadic arguments, they are first on par and then (vastly)
 Viacheslav> better than other ways of handling variadic arguments.

Given:

local function foo1(f,...)
	local function drop1(s,...)
		if s then
			return ...
		else
			return
		end
	end
	drop1(f(...))
end

local function foo2(f,...)
	local r = table.pack(f(...))
	if r[1] then
		return table.unpack(r, 2, r.n)
	else
		return
	end
end

then averaged over a large number of calls, with 5 to 50 results in
the list, foo2 is around 3x slower than foo1. The proportional speed
difference does not seem to be narrowing for longer argument lists.
(For short lists the difference is narrower, but the non-table version
is always at least 2x faster.)

Now, for something other than "drop the first result" which happens to
be easy without needing a table, it might well be simpler to use a table
(dropping the last result, for example, would require a lot of
recursion).

-- 
Andrew.