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From aalexandrov <...@git.apache.org>
Subject [GitHub] flink pull request: [FLINK-2809] [scala-api] Added UnitTypeInfo an...
Date Sat, 17 Oct 2015 10:18:52 GMT
Github user aalexandrov commented on the pull request:

    https://github.com/apache/flink/pull/1217#issuecomment-148901986
  
    > Not all methods without paremeters should translate to methods without parenthesis...
    
    @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:
    
    ```scala
    // 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?


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