Array Access

	Programming in Lua
	Part IV. The C API              Chapter 28. User-Defined Types in C

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28.4 - Array Access

An alternative to the object-oriented notation
is to use a regular array notation to access our arrays.
Instead of writing a:get(i),
we could simply write a[i].
For our example, this is easy to do,
because our functions setarray and getarray
already receive their arguments in the order that they
are given to the respective metamethods.
A quick solution is to define those metamethods right into our Lua code:

    local metaarray = getmetatable(newarray(1))
    metaarray.__index = array.get
    metaarray.__newindex = array.set

(We must run that code on the original implementation for arrays,
without the modifications for object-oriented access.)
That is all we need to use the usual syntax:

    a = array.new(1000)
    a[10] = 3.4         -- setarray
    print(a[10])        -- getarray   --> 3.4

If we prefer, we can register those metamethods in our C code.
For that, we change again our initialization function:

    int luaopen_array (lua_State *L) {
      luaL_newmetatable(L, "LuaBook.array");
      luaL_openlib(L, "array", arraylib, 0);
    
      /* now the stack has the metatable at index 1 and
         `array' at index 2 */
      lua_pushstring(L, "__index");
      lua_pushstring(L, "get");
      lua_gettable(L, 2);  /* get array.get */
      lua_settable(L, 1);  /* metatable.__index = array.get */
    
      lua_pushstring(L, "__newindex");
      lua_pushstring(L, "set");
      lua_gettable(L, 2); /* get array.set */
      lua_settable(L, 1); /* metatable.__newindex = array.set */
    
      return 0;
    }

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Programming in Lua