Re: Discriminants of tagged types

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 30 Paź, 22:21, "Vinzent Hoefler" <nntp-2010...@t-domaingrabbing.de>
wrote:

> > No. File descriptors are just indices into some array of objects
> > managed by the operating system.
>
> Maybe they are, maybe they aren't. How are you supposed to know that?

I've read that on Wikipedia:

http://en.wikipedia.org/wiki/File_descriptor

;-)

File descriptor is called a file descriptor and not just a file,
because, well, it is a descriptor and not a file.

> Given an opaque type, how can you tell the difference? The set of
> visible operations is the same.

Almost. Descriptors become dangling when the actual objects cease to
exist - and this dangling state can be detected via their public
interface (perhaps only via errors). The actual objects never dangle,
only their descriptors (this concept includes pointers, names, etc.)
can do it.

> IMO polymorphism and copy semantics are distinct
> concepts.

As already said, I've yet to see a convincing example of a type that
is both justifiably polymorphic and copyable at the same time.

--
Maciej Sobczak * http://www.inspirel.com