1.5.md

functions can be overloaded

function mymax(a, b)
	return ((a>b) and a) or b
end

mymax(1) --> mymax (1, nil)
mymax(1,2,3) --> mymax (1,2), 3 is discarded

e.g.

function inc (n)
	n = n or 1
	count = count + n
end

multiple return values

s, e = string.find("hello lua users", "lua")

return a,b

a special function unpack(), which can be used as generic call mechanism.

function unpack (t, i)
	i = i or 1
	if t[i] then
		return t[i], unpack (t, i+1)
	end
end

variable number of arguments

function add (...)
	local s = 0
	for i, v in ipairs {...} do
		s = s + v
	end
	return s
end

print (add(1,2,3,4,5,6))

-- original
function foo (a, b, c)

-- alternative, perl-like
function foo (...)
	local a, b, c = ...
	-- STUFF
end

multi-value identity

function id (...) return ... end

debug/trace use example

function foo_debug (...)
	print ("I: Calling foo(", ..., ")")
	return foo (...)
end

function fwrite (fmt, ...)
	return io.write (string.format(fmt, ...))
end

sometimes the argument list contains some nil, at that time select() should be used.

for i = 1, select ('#', ...) do --> select('#',...) returns the total size of the argument list, including nil.
	local arg = select (i, ...) --> fetch the i-th argument
	STUFF
end

named arguments

rename (old="temp.lua", new="temp1.lua") is not supported directly in Lua.

function rename (arg)
	return os.rename (arg.old, arg.new)
end

rename ({old = "temp.lua", new = "temp1.lua"}) --> "(" ")" can be omitted.