• Mehrdad (6/6) Jun 12 2011 Is there any particular reason that structs and unions can't implement
• Jonathan M Davis (16/24) Jun 12 2011 They aren't virtual. For an interface to work, it has to be virtual. str...
• Andrei Alexandrescu (6/18) Jun 12 2011 He must be referring to nominal conformance. It's been discussed many
• Mehrdad (8/19) Jun 12 2011 Yeah I was referring to something similar to what C# has (aside from the...
• Max Klyga (5/27) Jun 13 2011 In C# compiler can do stuff that you are not allowed to do, such as

Mehrdad <wfunction hotmail.com> writes:

Is there any particular reason that structs and unions can't implement
interfaces?

If that was possible, template conditions could become much simpler
for a variety of cases, such as for checking if something is a
particular type of range or container.

Thoughts?

Jonathan M Davis <jmdavisProg gmx.com> writes:

On 2011-06-12 18:20, Mehrdad wrote:
 Is there any particular reason that structs and unions can't implement
 interfaces?
 
 If that was possible, template conditions could become much simpler
 for a variety of cases, such as for checking if something is a
 particular type of range or container.
 
 Thoughts?

They aren't virtual. For an interface to work, it has to be virtual. structs 
are value types, not reference types. They have no virtual table and have no 
polymorphism.

At best, there could be a way to indicate that a struct happens to have 
functions which match what the interface has, which could then be used for 
static instrospection, but you could never actually use a struct as an 
interface. But there is not currently any way to use an interface to check 
whether a struct implements a particular set of functions. And while eponymous 
templates such as isForwardRange could be simplified with such a feature, 
their usage would be the same, so it might help, but it wouldn't really help 
with template constraints. Not to mention, interfaces are likely to be far 
stricter about types than templates are, so it might be difficult to get that 
to work generically. Regardless, I'm very leery of associating interfaces and 
structs in any way shape or form, because they are _very_ different things.

- Jonathan M Davis

Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:

On 6/12/11 8:28 PM, Jonathan M Davis wrote:
 On 2011-06-12 18:20, Mehrdad wrote:
 Is there any particular reason that structs and unions can't implement
 interfaces?

 If that was possible, template conditions could become much simpler
 for a variety of cases, such as for checking if something is a
 particular type of range or container.

 Thoughts?

 They aren't virtual. For an interface to work, it has to be virtual. structs
 are value types, not reference types. They have no virtual table and have no
 polymorphism.

He must be referring to nominal conformance. It's been discussed many 
times. There are important disadvantages (e.g. you can't "implement" a 
type alias) but there are advantages too.

Ultimately we never got around to it.


Andrei

Mehrdad <wfunction hotmail.com> writes:

lack of boxing).

On 6/12/2011 6:46 PM, Andrei Alexandrescu wrote:
 On 6/12/11 8:28 PM, Jonathan M Davis wrote:
 They aren't virtual. For an interface to work, it has to be virtual. 
 structs
 are value types, not reference types. They have no virtual table and 
 have no
 polymorphism.



still work pretty well (e.g. foreach loops work with List<T>.Enumerator, 
which is a struct but which can be treated as the IEnumerator<T> 
interface), right?

 He must be referring to nominal conformance. It's been discussed many 
 times. There are important disadvantages (e.g. you can't "implement" a 
 type alias) but there are advantages too.
 Ultimately we never got around to it.

 Andrei

Haha ok, that's a good reason in its own way, thanks. :)

Max Klyga <max.klyga gmail.com> writes:

On 2011-06-13 06:21:47 +0300, Mehrdad said:


 the lack of boxing).
 
 On 6/12/2011 6:46 PM, Andrei Alexandrescu wrote:
 On 6/12/11 8:28 PM, Jonathan M Davis wrote:
 They aren't virtual. For an interface to work, it has to be virtual. structs
 are value types, not reference types. They have no virtual table and have no
 polymorphism.


 

 they still work pretty well (e.g. foreach loops work with 
 List<T>.Enumerator, which is a struct but which can be treated as the 
 IEnumerator<T> interface), right?


autoboxing structs in objects to allow Interface usage, calling Object 
methods or some magic duck typing. In most cases it devirtualizes 
calls, so there is no overhead in boxing.
 
 He must be referring to nominal conformance. It's been discussed many 
 times. There are important disadvantages (e.g. you can't "implement" a 
 type alias) but there are advantages too.
 Ultimately we never got around to it.
 
 Andrei

 
 Haha ok, that's a good reason in its own way, thanks. :)