_call me, please

["Foreman, Bill" <billf@...>]

Need help,

 

I have a built-in module for complex numbers defined as follows:

 

int complex_number_new(lua_State* L)

{

      // make a complex number and put it on the stack

      return 1;

}

 

 

static const struct luaL_Reg s_complex_f[] =

{

      // constructor

      { "new", complex_number_new },

 

      // many more functions …     

      { 0, 0 }

};

 

 

static const struct luaL_Reg s_complex_m[] =

{

      { "__call", complex_number_new },

 

      // many more operators …

      { 0, 0 }

};

 

 

int luaopen_complex_number(lua_State* L)

{

      //

      luaL_newmetatable(L, "ak_complex");

 

      //

      luaL_register(L, 0, s_complex_m);

      luaL_register(L, "complex", s_complex_f);

 

      return 1;

}

 

 

Question:  Why do I get the error “attempt to call global ‘complex’ (a table value)” when I attempt x = complex (1, 2), which should return the same thing as complex.new(1, 2)?

 

I see this question in the forum, but I (for the life of me) don’t understand the responses.  What is special about __call, and why isn’t it better documented?  I am so thick that it is going to take a concrete example in c or c++ to breach the wall.

 

What does work is

setmetatable(complex, { __call = function( _, ... ) return complex.new( ... ) end })

 

but I want to do this internally, not in Lua.

 

--BillF