Re: preventing a library from being modified

[Coda Highland <chighland@...>]

On Thu, Mar 23, 2017 at 12:58 PM, pierre <pierre.saunier@ppmodeler.com> wrote:
> Hi,
>
> I am trying to protect a library from being modified... but without success.
>
> Basically, I am creating a newindex function:
> static int luaA_library_newindex(lua_State *L)
> {
>   lua_pushstring(L, "library: package cannot be modified");
>   lua_error(L);
>   return 0;
> }
>
> then, I am creating a metatable, assign it the the library (a table) and set
> its __newindex:
> int luaA_open_library(lua_State *L)
> {
>   luaL_newmetatable(L, "library");
>
>   lua_pushstring(L, "__index");
>   lua_pushvalue(L, -2);  // pushes the metatable
>   lua_settable(L, -3);  // metatable.__index = metatable
>
>   lua_pushstring(L, "__newindex");
>   lua_pushcfunction(L, luaA_library_newindex);
>   lua_settable(L, -3);  // metatable.__newindex = func
>
>   luaL_openlib(L, "library", luaA_library_f, 0);
>
>   luaL_getmetatable(L, "library");
>   lua_setmetatable(L, -2); // library.metatable = metatable
> }
>
>
> the problem is, it is preventing to add new values to the library table but
> not to modify existing ones...
> How can I prevent to modify existing entries?
>
>
> Thanks,
> Craouette

Create a proxy table that passes through accesses to the library, so
that it doesn't itself contain any keys -- that way all writes trigger
newindex.

/s/ Adam