View mode: basic / threaded / horizontal-split · Log in · Help
April 01, 2012
Nested interface
I was working on a small personal project, and ran across 
something I think might (or might not) be a bug.  I'm posting in 
this particular group just in case it's a restriction somewhere 
that I just don't know about, or maybe just the way that 
covariance gets resolved.  The obvious workaround is to return 
NestedInterface from the two methods of the derived class rather 
than NestedImplementation, but I was kind of surprised it didn't 
compile (in the actual code, both the nested interface and the 
nested implementation were called "Node" which was stupid on my 
part).  I got the error message:  "Error: class 
Implementation.NestedImplementation ambiguous virtual function 
getNext"

Is this something anyone is likely to care about?

shared interface Interface
{
	public static shared interface NestedInterface
	{
		public shared(NestedInterface) getNext();
		public shared(const(NestedInterface)) getNext() const;
	}
}

shared class Implementation : Interface
{
	public static shared class NestedImplementation : 
Interface.NestedInterface
	{
		public override shared(NestedImplementation) getNext()
		{
			return null;
		}

		public override shared(const(NestedImplementation)) getNext() 
const
		{
			return null;
		}
	}
}
April 01, 2012
Re: Nested interface
Hm, I guess it's much simpler than that.  I must not be 
understanding something about covariance.  The following code 
produces the same error message (it has nothing to do with 
nestedness or shared classes):


interface Interface
{
	Interface getNext();
	const(Interface) getNext() const;
}

class Implementation : Interface
{
	Implementation getNext()
	{
		return null;
	}

	const(Implementation) getNext() const
	{
		return null;
	}
}


On Sunday, 1 April 2012 at 16:40:55 UTC, Read Bixby wrote:
> I was working on a small personal project, and ran across 
> something I think might (or might not) be a bug.  I'm posting 
> in this particular group just in case it's a restriction 
> somewhere that I just don't know about, or maybe just the way 
> that covariance gets resolved.  The obvious workaround is to 
> return NestedInterface from the two methods of the derived 
> class rather than NestedImplementation, but I was kind of 
> surprised it didn't compile (in the actual code, both the 
> nested interface and the nested implementation were called 
> "Node" which was stupid on my part).  I got the error message:  
> "Error: class Implementation.NestedImplementation ambiguous 
> virtual function getNext"
>
> Is this something anyone is likely to care about?
>
> shared interface Interface
> {
> 	public static shared interface NestedInterface
> 	{
> 		public shared(NestedInterface) getNext();
> 		public shared(const(NestedInterface)) getNext() const;
> 	}
> }
>
> shared class Implementation : Interface
> {
> 	public static shared class NestedImplementation : 
> Interface.NestedInterface
> 	{
> 		public override shared(NestedImplementation) getNext()
> 		{
> 			return null;
> 		}
>
> 		public override shared(const(NestedImplementation)) getNext() 
> const
> 		{
> 			return null;
> 		}
> 	}
> }
April 01, 2012
Re: Nested interface
On 04/01/2012 08:13 PM, Read Bixby wrote:
> Hm, I guess it's much simpler than that.  I must not be understanding
> something about covariance.  The following code produces the same error
> message (it has nothing to do with nestedness or shared classes):
>
>
> interface Interface
> {
>      Interface getNext();
>      const(Interface) getNext() const;
> }
>
> class Implementation : Interface
> {
>      Implementation getNext()
>      {
>          return null;
>      }
>
>      const(Implementation) getNext() const
>      {
>          return null;
>      }
> }
>

This is a compiler bug. It works if 'Interface' is changed to an 
abstract class.

Please report this issue to the bug tracker:
http://d.puremagic.com/issues/
April 01, 2012
Re: Nested interface
Thanks; entered as issue 7807.

On Sunday, 1 April 2012 at 20:17:09 UTC, Timon Gehr wrote:
> On 04/01/2012 08:13 PM, Read Bixby wrote:
>> Hm, I guess it's much simpler than that.  I must not be 
>> understanding
>> something about covariance.  The following code produces the 
>> same error
>> message (it has nothing to do with nestedness or shared 
>> classes):
>>
>>
>> interface Interface
>> {
>>     Interface getNext();
>>     const(Interface) getNext() const;
>> }
>>
>> class Implementation : Interface
>> {
>>     Implementation getNext()
>>     {
>>         return null;
>>     }
>>
>>     const(Implementation) getNext() const
>>     {
>>         return null;
>>     }
>> }
>>
>
> This is a compiler bug. It works if 'Interface' is changed to 
> an abstract class.
>
> Please report this issue to the bug tracker:
> http://d.puremagic.com/issues/
Top | Discussion index | About this forum | D home