super-interfaces

[Chris Nicholson-Sauls]

Bill Baxter wrote:
> Chris Nicholson-Sauls wrote:
>> Bill Baxter wrote:
>>> I think this may be a bug with super-interfaces.
>>> It's telling me that something is not an override, when, in fact, it is.
>>>
>>> Here's the setup:
>>>
>>> interface Fruit
>>> {
>>>    ...  // some methods
>>> }
>>> interface Vehicle
>>> {
>>>    void drive_around();
>>>    ...  // some other methods
>>> }
>>> interface MobileFruit : Fruit, Vehicle
>>> {
>>>    // nothing here, should inherit from superinterfaces
>>> }
>>>
>>> class BaseFruit : Fruit
>>> {
>>>    // implement (some of) Fruit's methods here
>>> }
>>>
>>> class MobileFruitGundam : BaseFruit, MobileFruit
>>> {
>>>    // implement what's not in BaseFruit already
>>>
>>>    override void drive_around() {..} // from Vehicle
>>> }
>>>
>>> The last part doesn't work.  It tells me that drive_around is not an 
>>> override.  But it works if I don't tag it with 'override'.
>>>
>>> Is that a bug?
>>>
>>> --bb
>>
>> I don't think it is.  As I understand it, 'override' only masks a 
>> virtual function implementation or 'abstract' placeholder.  Interfaces 
>> do not provide implementations nor placeholders, only a contract 
>> requiring certain signatures exist.  The main use of 'override' is to 
>> catch non-back-compatible API changes.
>>
>> -- Chris Nicholson-Sauls
> 
> Huh, well I routinely use override on things I inherit from interfaces.
> 
> This generates no errors:
> interface Fruit
> {
>     void eat();
> }
> class YummyFruit : Fruit
> {
>     override void eat() {
>        writefln("That's yummy");
>     }
> }
> 
> So you're opinion is that the spec says that should be an error?
> 
> --bb

Essentially... yeah.  :)  Quoting the 'Attributes' page:
"""The override attribute applies to virtual functions. It means that the function must 
override a function with the same name and parameters in a base class."""

So, to me, that means interfaces are excluded from 'override's behavior.  Although the 
fact that your simpler example works makes me wonder.  (I'd never actually tried it.)

-- Chris Nicholson-Sauls