Wrapping C functions into nested Lua tables
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- Subject: Wrapping C functions into nested Lua tables
- From: Seba <lseba@...>
- Date: 2015年7月11日 15:46:11 +0200
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