Casting to interface not allowed in @safe code?

[Nathan S.]

On Tuesday, 21 May 2019 at 07:59:13 UTC, Jim wrote:
> On Tuesday, 21 May 2019 at 07:33:17 UTC, rumbu wrote:
>> On Tuesday, 21 May 2019 at 07:16:49 UTC, Jim wrote:
>>> On Tuesday, 21 May 2019 at 07:04:27 UTC, rumbu wrote:
>>>> On Tuesday, 21 May 2019 at 05:51:30 UTC, Jim wrote:
>>>>
>>>> That's because foo is of type Base, not implementing 
>>>> FeatureX.
>>>
>>> Right, Base isn't implementing FeatureX, but foo is really a 
>>> Foo
>>
>> That's your knowledge, for the compiler foo is really a Base, 
>> as written in your own code.
>>
>
> Yes, thinking about it again it makes sense.

It doesn't even slightly make sense. I just ran into this today 
myself. Unlike Java and C#, casting from Foo to FeatureX is not 
an assertion that the Foo implements FeatureX. Instead it's how 
you test at runtime if the class of a specific object derived 
from Foo implements FeatureX: if it doesn't then the result of 
the cast is null. I've opened a bug report at 
https://issues.dlang.org/show_bug.cgi?id=20000.