Surprising behavior of table.insert()

[Hisham <hisham.hm@...>]

Hi list,

I bumped into a behavior that surprised me today. I have a function
that may or may not return a value, and insert that value into a
table. Given that Lua ignores extra arguments and fills missing
arguments with nil, I expected that I could just do

   table.insert(my_table, my_function())

But I got "wrong number of arguments to 'insert'". What surprised me
the most, however, was that while passing a nil variable is allowed,
passing a nullary function is frowned upon:

Lua 5.1.3  Copyright (C) 1994-2008 Lua.org, PUC-Rio
> t = {}
> x = nil
> table.insert(t, x)
> f = function() end
> table.insert(t, f())
stdin:1: wrong number of arguments to 'insert'
stack traceback:
        [C]: in function 'insert'
        stdin:1: in main chunk
        [C]: ?
>

I understand the mechanics of this behavior (one pushes nil to the
stack as opposed to pushing nothing, as can be demonstrated with
select()), but I wonder if this extra check in table.insert doesn't go
somewhat against the general behavior of parameter-passing in Lua
(where missing arguments are filled with nil), given that nil is a
valid value for the argument in this function.

-- Hisham