Re: inhibit compiler warning C4624 for a class hierarchy

"Igor Tandetnik" <>
Tue, 16 Jan 2007 18:07:17 -0500
Ben Voigt <rbv@nospam.nospam> wrote:

It appears that none of your classes are actually POD types.
Luckily, you don't need to meet a higher bar of using only POD
types: it should be sufficient for your purposes to have types with
trivial constructor and destructor. In particular, you can use
inheritance, but you shouldn't have any user-declared constructors
or destructors.

... as well all non-static data members should have trivial
constructors and destructors, which is why today I wrote "the
hierarchy will permit only POD members"... which seems to be an
essential part of the lower bar you speak of.

You seem to be using the term POD as a shortcut for "a fundamental type,
or a class with trivial constructor and destructor". Any POD struct has
trivial constructor and destructor, but not every one with trivial
constructor and destructor is POD.

For a structure to have a trivial constructor, it is necessary that all
its members also have a trivial constructor. They don't have to be PODs
(e.g. they could be classes derived from other classes, or have private
members). E.g.

struct A { int x; }; // POD
struct B : public A { int y; }; // not a POD
struct C { A a; B b; }; // not a POD

A, B and C all have trivial constructors and destructors. Only A is a
POD-struct. For all three it is legal to do something like

C* pc = (C*)malloc(sizeof(C));
// do something to pc


What's also needed is a noinherit keyword for class members that
affects name visibility, especially overload resolution, but not
struct X
   noinherit static int x;
   static int y;
   noinherit enum { xxx = 1; }
   noinherit int f(int);

struct Y : public X
   void f(double);
   void test() {
       x; // not allowed
       X::x; // ok

I'm not sure how this is useful.

       xxx; // not allowed
       __super::xxx; // ok

What would '__super' mean in the presense of multiple inheritance? In
any case, I still don't see how this construct is useful.

       f(1); // calls Y::f(double)

So it does now, without any new keyword.
With best wishes,
    Igor Tandetnik

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