> On Jun 28, 2016, at 1:25 PM, Dan Debrunner <[email protected]> wrote:
>
> On 6/28/2016 7:06 AM, Dale LaBossiere wrote:
>>
>
>> The union() gets a compilation error because TStream<Derived*> doesn't extend
>> TStream<Base>. Std java generics stuff. A straightforward cast doesn't
>> work;
>> it requires a bit more convoluted casting.
>
> I wonder if the signature of the union should change in someway, or an
> overload of the union.
perhaps such as… ?
And it seems like the issue is larger than just union().
Related to the last question / answer, if there are both base-analytics and
derived analytics (and there was no union involved):
TStream<Derived> sD = …; // ingest
derivedAnalytics(sD);
baseAnalytics(sD); // still want/need something like:
baseAnalytics(sD.cast(Base.class));
>
>>
>> We could make this much easier for users if we added:
>> TStream<T>:
>> // typesafe cast a TStream<T> to a TStream<U>
>> // compile error if U doesn't extend T
>> <U extends T> TStream<U> cast(Class<U> classU);
>
> Isn't it the case that T is a sub-class of U, so T extends U?
Yup. typo when transcribing, here and below :-) Sorry for the confusion.
>
>> Then one could write:
>> TStream<Base> sBase = sDerived1.cast(Base.class).union(
>> sDerived2.cast(Base.class) );
>>
>> Does this seem like the right thing to do? Alternatives?
>>
>> Fwiw, the implementation of cast() is trivial once you know what to do:
>> <U extends T> TStream<U> cast(Class<U> classU) {
>> TStream<?> s = (TStream<?>) this;
>> @SuppressWarnings("unchecked")
>> TStream<U> u = (TStream<U>) s;
>> return u;
>> }
>
> This just feels wrong, given that T is a sub-class of U that one has to do
> unchecked casts.
Did I miss something?
The actual static method I wrote/played with is (now simplified as I see the
cast to <?> didn’t help):
static <T extends U,U> TStream<U> cast(TStream<T> s, Class<U> classU) {
@SuppressWarnings("unchecked")
TStream<U> u = (TStream<U>) s;
return u;
}
Even though T extends U the compiler warns without the suppress.
>
> Any reason why the original streams were just not declared with the base type?
Yes. Imagine there are both base-type analytics and derived-type analytics.
Where does that leave us?
— Dale
