Re: [ Lua C API ] lua_upvalueid - index > # upvalues?

[Viacheslav Usov <via.usov@...>]

On Sat, Sep 26, 2020 at 3:23 PM JeanHeyd Meneide
<phdofthehouse@gmail.com> wrote:

> So... what happens if you do?

Here is what the code does:

LUA_API void *lua_upvalueid (lua_State *L, int fidx, int n) {
  StkId fi = index2addr(L, fidx);
  switch (ttype(fi)) {
    case LUA_TLCL: {  /* lua closure */
      return *getupvalref(L, fidx, n, NULL);
    }
    case LUA_TCCL: {  /* C closure */
      CClosure *f = clCvalue(fi);
      api_check(L, 1 <= n && n <= f->nupvalues, "invalid upvalue index");
      return &f->upvalue[n - 1];
    }
    default: {
      api_check(L, 0, "closure expected");
      return NULL;
    }
  }
}

And here is another bit:

typedef struct CClosure {
  ClosureHeader;
  lua_CFunction f;
  TValue upvalue[1];  /* list of upvalues */
} CClosure;

If the implications are not obvious, you should just follow the manual :)

Cheers,
V.