Lua Function Paramters

When a function is called, the list of arguments is adjusted to the length of the list of parameters, unless the function is a variadic or vararg function, which is indicated by three dots ('...') at the end of its parameter list. A vararg function does not adjust its argument list; instead, it collects all extra arguments and supplies them to the function through a vararg expression, which is also written as three dots. The value of this expression is a list of all actual extra arguments, similar to a function with multiple results. If a vararg expression is used inside another expression or in the middle of a list of expressions, then its return list is adjusted to one element. If the expression is used as the last element of a list of expressions, then no adjustment is made (unless that last expression is enclosed in parentheses).

As an example, consider the following definitions:

    function f(a, b) end
    function g(a, b, ...) end

Then, we have the following mapping from arguments to parameters and to the vararg expression:

    CALL            PARAMETERS
    
    f(3)             a=3, b=nil
    f(3, 4)          a=3, b=4
    f(3, 4, 5)       a=3, b=4
    f(r(), 10)       a=1, b=10
    f(r())           a=1, b=2
    
    g(3)             a=3, b=nil, ... -->  (nothing)
    g(3, 4)          a=3, b=4,   ... -->  (nothing)
    g(3, 4, 5, 8)    a=3, b=4,   ... -->  5  8
    g(5, r())        a=5, b=1,   ... -->  2  3

See http://www.lua.org/manual/5.1/manual.html#2.5.8 for more details.