Wrapping C functions into nested Lua tables

[Seba <lseba@...>]

Hello!

I'm currently diving into Lua's C API, and try to set up an example 
"shapes" library that allows me to create shapes (such as rectangles, 
triangles, etc.), and use methods on them, such as "get_width()" and 
similar.

This is the way I would like to use the library:

shapes = require "shapes"

rect = shapes.rectangle.new()
print(rect:get_width())

tri = shapes.triangle.new()
print(tri:get_width())


Chapter 29 of PIL teaches me how to set up a single "rectangle" table 
that I can use like this:

shapes = require "shapes"

rect = shapes.new()
print(rect:get_width())

Using the following C code:

/* ... */

int luaopen_shapes(lua_State *L) {
    luaL_newmetatable(L, "rectangle");
    luaL_setfuncs(L, rectangle_m, 0);
    luaL_newlib(L, rectangle_f);
    return 1;
}


However, I'm unsure how I can put my separate "triangle" and "rectangle" 
tables into a parent table. All examples I've found so far either use a 
single table (like "shapes.new()" instead of "shapes.rectangle.new()") 
or use functions prior to Lua 5.2. However, I would like to know how to 
do this in Lua 5.2/5.3 that don't support luaL_register() anymore (as 
far as I understand).

I had some luck using the following setup inside luaopen_shapes():

lua_newtable(L);
luaL_newmetatable(L, "rectangle");
luaL_setfuncs(L, rectangle_m, 0);
luaL_newlib(L, rectangle_f);
lua_setfield(L, -2, "rectangle");


However, when I create an object using "shapes.rectangle.new()" this 
way, I can't access it's methods: rectangle:get_width()

I probably put the tables and metatables on the stack in a wrong order. 
I would be very grateful if someone could show me the right order.

Kind regards