Traits

[Jonathan M Davis]

On Friday, October 11, 2013 22:31:25 Jonathan M Davis wrote:
> On Saturday, October 12, 2013 00:54:48 luminousone wrote:
> > The inability to handle null is pretty big, specially considering
> > that at not point is the class instance itself cared about!,
> 
> No. It's expected. When you are casting to a particular object to test
> whether the object is of that type, you are testing the type that the
> object is, and if the object is null, then it is _not_ of the type that
> you're casting to.
> > Again this should be done via reflection, this method above is
> > hackish at best.
> 
> Testing via compile-time reflection is testing for something fundamentally
> different than what casting is testing for. With casting, you're testing
> whether the object is the type that you're casting to or a type derived from
> the type that you're casting to. With compile-time reflection, you're
> testing whether a particular type is derived from another type. One is
> testing an instance. The other is testing a type. The two are completely
> different.

I'd also point out that if you have

class A
{
}

class B : A
{
}

B is _not_ an instance of A. It's a subclass of A. An instance is an object in 
memory, not the type of the object.

auto a = new A; //instance of A
auto b = new B; //instance of B
A c = new B; //instance of B
A d; //There is no instance here. The reference is null.
B e; //There's no instance here either for the same reason.

So, you're using the term "instance of" incorrectly.

- Jonathan M Davis