Function

Default Return

Lua function returns nil as default.

print((function() end)() == nil) -- true

Variadic Parameter

Variadic parameter in lua does not have name and default type, it's a special identifier ... that has to be expanded to a table using { ... }

Such identifier can be used in:

• { ... }: direct expansion
• { a, ..., b }: append extra items around
• select('#', ...) and select(idx, ...) to get length or pick one item of the args without intermediate expansion

local function foo(...)
  local args = { ... }
  print(table.concat(args, ', '))
end

foo('hello', 'world') -- hello, world

Iterate over variadic without expansion
local function foo(...)
  for idx = 1, select('#', ...) do
    _ = select(idx, ...)
  end
end

Multi-Returns

local function foo()
  return 1, 2, 3
end

local a, b, c = foo()

Meta Functions

Mate Functions are global functions registered by lua runtime but commonly used

• _G.select: an operator can perform item picking from arbitrary number of arguments including ... or get length of args

  -- get length of args
  _ = select('#', 1, 2, 3) -- 3
  -- pick second item
  _ = select(2, 1, 2, 3) -- 2

• _G.unpack: equivalent to table.unpack