Am 06.06.2013 00:37, schrieb Steven Schveighoffer:
On Wed, 05 Jun 2013 18:32:58 -0400, Adam D. Ruppe
<destructiona...@gmail.com> wrote:
On Wednesday, 5 June 2013 at 22:03:05 UTC, Walter Bright wrote:
1. Introduce 'virtual' storage class. 'virtual' not only means a
method is virtual, but it is an *introducing* virtual, i.e. it starts
a new vtbl[] entry even if there's a virtual of the same name in the
base classes. This means that functions marked 'virtual' do not
override functions marked 'virtual'.
Your upgrade path sounds generally good to me, I can live with that.
But I want to clearify this #1:
class A { virtual void foo(); }
class B : A { virtual void foo(); }
Error, yes? It should be "override void foo();" or "override final
void foo();".
(override and virtual together would always be an error, correct?)
Whereas:
class A { virtual void foo(); }
class B : A { virtual void foo(int); }
is OK because foo(int) is a new overload, right?
No, I think it introduces a new foo. Calling A.foo does not call
B.foo. In other words, it hides the original implementation, there are
two vtable entries for foo.
At least, that is how I understood the C# description from that post,
and it seems Walter is trying to specify that. The idea is that B
probably defined foo before A did, and A adding foo should not break B,
B didn't even know about A's foo.
-Steve
Here it is described the C# semantics for virtual methods
http://msdn.microsoft.com/en-us/library/6fawty39.aspx
