Hello,
Just copying my answer on Stackoverflow to the user-group:
Unfortunately, Java does not know declaration-site variance like C# or
Scala:
// C# styleinterface Result<out Record> { ... }
// Scala style
trait Result[+Record] { ... }
Both of the above would allow assigning the following
Result<Record4<T1, ...>> r1 = ...Result<Record> r2 = r1;
But Result <http://www.jooq.org/javadoc/latest/org/jooq/Result.html> is
really defined as:
interface Result<R extends Record> {}
Now, since your query expression binds <R> to Record4<T1, ...>, this is
what you're going to get:
Result<Record4<T1, ...>> r1 = selectDistinct(...).fetch();
Alternatively, you can just use a wild-card
Result<? extends Record> r2 = r1;
// Or shorter:Result<?> r3 = r1;
Another option is to force removal of typesafety when expressing your query:
Result<Record> r4 = selectDistinct(new Field[] { ... }).fetch();
Source: http://stackoverflow.com/a/20727581/521799
J.B. Nizet's answer has some more insight into how Java generics work:
http://stackoverflow.com/a/20727510/521799
2013/12/22 bruce buchanan <[email protected]>
> I'm using pretty standard syntax here, I think:
>
> Result<Record> = ...selectDistinct(...).fetch();
>
> but it wont compile because the above returns Result<Record4<...>> which
> is an autogenerated interface, which is a subinterface of Record but the
> compiler remains unhappy
>
> I suppose normally java will treat this as an implicit cast? doesnt seem
> like I should be doing any explicit casting?
>
> thanks
>
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