On Thursday, 30 January 2014 at 17:38:26 UTC, Steven
Schveighoffer wrote:
On Thu, 30 Jan 2014 12:30:04 -0500, Frustrated
<c1514...@drdrb.com> wrote:
On Thursday, 30 January 2014 at 17:11:24 UTC, Steven
Schveighoffer wrote:
On Thu, 30 Jan 2014 11:58:15 -0500, Frustrated
<c1514...@drdrb.com> wrote:
Essentially what it boils down to is treating interfaces like
classes that have no fields). To avoid the diamond problem
simply
always choose the method that is not from the
interface(since it
is "default"), which is done naturally with the vtable.
It's simpler than that. A function is a block of code. A
vtable entry points to a block of code. Just point the vtable
entry at the block of code that is the default implementation.
-Steve
Right, this was my original point and why I thought there was
already entries for the interface in the vtable(since I seemed
to
have called some function that did nothing when it should
have).
I think your original example should not have happened. Either
there was a bug in the runtime, compiler, or your memory :)
Well, as usual, it is almost surely user error. I can't reproduce
it so we'll just go with that.
It seems so simple and offers some benefit(would at the very
least stop requiring one to implement a class every time they
want test a design. When programming to interfaces and using
some
type of factory it makes even more sense.
This is a misunderstanding, you still need to declare a class,
because an interface is not a concrete type. But if there are
default implementations for all the interface functions, you
don't need to implement any of them!
No, the point is, if all methods are defined, there is no need to
create the class. Why create an empty class to instantiate it
when the compiler can do it for you and you can instantiate the
interface? This is what I mean by treating the interface as a
class because for all purposes it is. (an interface is just an
abstract container but it doesn't have to be)
Again, all this could be done by the compiler internally by
creating a class to back an interface and add it to the vtable.
Instantiating the interface just returns that class. Calling a
member on the interface's object calls the member of that class,
who's body is provided in the interface definition.
I can do this now, the whole point is I don't like code
duplication! ;)
interface A
{
void foo() { writeln("me"); }
void bar();
}
class _A // created internally by compiler
{
void foo() { writeln("me"); } // added by compiler copied
from A
void bar() { assert(0, "error"); } // added by compiler
}
A a = new A; // reinterpreted by compiler as A a = new _A;
a.foo(); // prints me
a.bar(); // asserts
e.g., all we would see is
interface A
{
void foo() { writeln("me"); }
void bar();
}
which is much nicer on the eyes and about half the code.
One may argue that this blurs the lines between a class an
interface but it doesn't. It can still have multiple inheritance
but easily provide a default way to deal with stuff.
Remember, the whole point of interfaces was to solve diamond
problem. They also now provide the "contract"... I'm just trying
to get them to provide the "contract" with default behavior.
