Github user tillrohrmann commented on the pull request:
https://github.com/apache/flink/pull/1217#issuecomment-149137247
I think in the case of the UnitTypeInformation and the above-mentioned
methods which either return Unit or Boolean it is not a problem with the
parentheses because those types donât have a apply() method defined afaik.
However, we had before situations where methods returned a more complex
type which also defined an apply() method. In these cases foobar() with
definition def foobar: TypeWithEmptyApplyDefinition or def foobar():
TypeWithEmptyApplyDefinition have a different semantic behaviour. Since
this is hard to spot if you donât look at the definition of foobar and the
resulting type we decided to stick to a common pattern to always add
parentheses to overriden java methods. Of course, there are situations
where this is not needed but then the rule wouldnât be so simple anymore.
â
On Sat, Oct 17, 2015 at 12:18 PM, Alexander Alexandrov <
[email protected]> wrote:
> Not all methods without paremeters should translate to methods without
> parenthesis...
>
> @StephanEwen <https://github.com/StephanEwen> I agree with that, but I
> cannot understand how the UnitTypeInfo might cause a confusion here.
>
> The typeInformation macros are synthesized by the macro based on the
> inferred collection type, which means that the meaning of () is resolved
> before that. Consider the following example:
>
> // in the Scala REPL
> case class Foo(answer: Int)// defined class Foo
> def f1(): Foo = Foo(42)// f1: ()Foo
> def f2: Foo = Foo(42)// f2: Foo
> val xs = Seq(f1(), f2) // how a literate person would write it// xs:
Seq[Foo] = List(Foo(42), Foo(42))
> val xs = Seq(f1, f2) // how a dazed & confused person would write it, but
still compiles // xs: Seq[Foo] = List(Foo(42), Foo(42))
> val xs = Seq(f1, f2()) // even worse, but this breaks with a compiler
exception// error: Foo does not take parameters// val xs = Seq(f1, f2())
> val xs = Seq((), ()) // typing '()' without syntactic context resolves to
Unit// xs: Seq[Unit] = List((), ())
>
> In all of the above situations env.fromCollection(xs) is (1) either going
> to typecheck and trigger TypeInformation synthesis or (2) fail with the
> above.
>
> Can you point to StackOverflow conversation or something similar where the
> issue you mention is explained with an example?
>
> â
> Reply to this email directly or view it on GitHub
> <https://github.com/apache/flink/pull/1217#issuecomment-148901986>.
>
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