On 12/23/2014 10:17 PM, Andrei Alexandrescu wrote:
> On 12/23/14 8:54 PM, Walter Bright wrote:
>>
>> The current behavior of:
>>
>>      is (D : B)
>>
>> is the expression will evaluate to false if D does not compile. However,
>> a compile time error will be issued if B does not compile.
>>
>> If D and B compile, then it will evaluate to false if B is not
>> implicitly convertible to D. This suggests to me Option 1, i.e. if the
>> implicit conversion fails due to ambiguity errors, then it should return
>> false (not issue a compile time error).
>
> Though I agree it makes sense to just return false, I think it would be more
> sensible and useful to issue an error. If B is reachable from B through multiple
> paths, that's a new situation distinct from yes/no.

That would be inconsistent with how 'is' works for other types.


> In fact a better thought: as soon as D is defined, repeated subtyping should be
> detected as an error. Then there's no question about "is" in the first place :o).

That's a good idea, but I think it is unworkable. What is the set of types that B is implicitly convertible too? It's unbounded.

On 12/26/14 12:37 PM, Walter Bright wrote:
> On 12/23/2014 10:17 PM, Andrei Alexandrescu wrote:
>> In fact a better thought: as soon as D is defined, repeated subtyping
>> should be
>> detected as an error. Then there's no question about "is" in the first
>> place :o).
>
> That's a good idea, but I think it is unworkable. What is the set of
> types that B is implicitly convertible too? It's unbounded.

I think it's bounded. Example to the contrary? -- Andrei

On 26/12/14 19:53, Daniel N via Digitalmars-d wrote:
> Anyway considering the new ways of working, when using the -dip switch for the
> initial few releases, there is ample time to perfect all details.

Potentially related issue, regarding implicit conversion.  Given a struct as follows:

    struct Integer
    {
        int i_;

        alias i_ this;
    }

Can anyone explain to me why this works:

    Integer i = Integer(3);
    i = 5;

... but this doesn't:

    Integer i = 5;

It seems unintuitive, in the circumstances.

On Saturday, 27 December 2014 at 12:28:34 UTC, Joseph Rushton Wakeling wrote:
> On 26/12/14 19:53, Daniel N via Digitalmars-d wrote:
>> Anyway considering the new ways of working, when using the -dip switch for the
>> initial few releases, there is ample time to perfect all details.
>
> Potentially related issue, regarding implicit conversion.  Given a struct as follows:
>
>     struct Integer
>     {
>         int i_;
>
>         alias i_ this;
>     }
>
> Can anyone explain to me why this works:
>
>     Integer i = Integer(3);
>     i = 5;
>
> ... but this doesn't:
>
>     Integer i = 5;
>
> It seems unintuitive, in the circumstances.

Is "multiple alias this" implementation planned in near future? It could be useful for a project of mine :)

On Friday, 8 May 2015 at 13:57:56 UTC, Andrea Fontana wrote:
> On Saturday, 27 December 2014 at 12:28:34 UTC, Joseph Rushton Wakeling wrote:
>> On 26/12/14 19:53, Daniel N via Digitalmars-d wrote:
>>> Anyway considering the new ways of working, when using the -dip switch for the
>>> initial few releases, there is ample time to perfect all details.
>>
>> Potentially related issue, regarding implicit conversion.  Given a struct as follows:
>>
>>     struct Integer
>>     {
>>         int i_;
>>
>>         alias i_ this;
>>     }
>>
>> Can anyone explain to me why this works:
>>
>>     Integer i = Integer(3);
>>     i = 5;
>>
>> ... but this doesn't:
>>
>>     Integer i = 5;
>>
>> It seems unintuitive, in the circumstances.
>
> Is "multiple alias this" implementation planned in near future? It could be useful for a project of mine :)

I need it too, and also do static inheritance.
http://wiki.dlang.org/DIP84

On Monday, 27 June 2016 at 00:13:46 UTC, mogu wrote:
> On Friday, 8 May 2015 at 13:57:56 UTC, Andrea Fontana wrote:
>> Is "multiple alias this" implementation planned in near future? It could be useful for a project of mine :)
>
> I need it too, and also do static inheritance.
> http://wiki.dlang.org/DIP84

I implemented a limited version of multiple alias this:
https://github.com/mogud/MultiAliasThis/blob/master/mat.d

But it's only useful in composition. Static polymorphism(by implicit conversion in alias this) cannot work.