检测lua中的单个nil参数

Question

Is it possible to distinguish the call

myFunc()

from

myFunc(nil)

inside the function myFunc?

Answer 1

It is actually possible to distinguish a nil value from no value in Lua functions, providing they are expecting a variable number of arguments with the ... operator. It is not necessary very easy nor reasonable to exploit this, though. Example:

function myFunc(...)
  if select('#', ...) == 0 then
    print "Called without argument"
  elseif select('#', ...) == 1 and select(1, ...) == nil then
    print "Called with a nil argument"
  end
end