David B. Held wrote:
[...]
> and then just store Base*, but this requires explicit run-time
> checking of types which would otherwise be automatic with pointers to
> T instead of optional<T>. If this is the only solution, so be it;
> but any clever alternatives are welcome.
This example is not objective at all, but I think it would be possible to
add a convertion operator which will decide if the cast is acceptable or
not. It is not meant for pointers, but reference types:
struct A
{
virtual ~A() {}
};
struct B : A
{
};
struct C
{
};
template <typename T>
struct optional
{
template <typename U>
operator optional<U> const () const
{
return * reinterpret_cast<optional<U> const *>(static_cast<U
const *>(reinterpret_cast<T const *>(storage_)));
}
...
};
void foo(optional<A> const &)
{
}
int main()
{
optional<B> b;
optional<C> c;
foo(b);
//foo(c);
}
Philippe A. Bouchard
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