Re: Sammy + wildcards + type inference = :(

Hi,

Yes, I'm still working on having type inference understand Java's use-site
variance in terms of Scala's definition-site variance. (Here's a good paper
<http://yanniss.github.io/varj-ecoop12.pdf> on the topic -- it's tricky :-))

Meanwhile, specifying the type arguments works around this limitation:

scala>  new java.util.ArrayList[String]().stream.map[Int](_.toInt)
res2: java.util.stream.Stream[Int] =
java.util.stream.ReferencePipeline$3@28dcca0c

scala> new
java.util.ArrayList[String]().stream.map[Int](_.toInt).map[String](_.toString)
res3: java.util.stream.Stream[String] =
java.util.stream.ReferencePipeline$3@6f7923a5

cheers
adriaan

On Fri, Jun 26, 2015 at 6:40 PM, Roman Janusz <[email protected]>
wrote:

> Not much of an improvement if I can't chain:
>
> scala> new
> java.util.ArrayList[String]().stream.map(_.toInt).map(_.toString):
> JStream[String]
> <console>:9: error: no type parameters for method map: (x$1:
> java.util.function.Function[_ >: String, _ <: R])java.util.stream.Stream[R]
> exist so that it can be applied to arguments
> (java.util.function.Function[String,Int] with Serializable)
>  --- because ---
> argument expression's type is not compatible with formal parameter type;
>  found   : java.util.function.Function[String,Int] with Serializable
>  required: java.util.function.Function[_ >: String, _ <: ?R]
> Note: String <: Any (and java.util.function.Function[String,Int] with
> Serializable <: java.util.function.Function[String,Int]), but Java-defined
> trait Function is invariant in type T.
> You may wish to investigate a wildcard type such as `_ <: Any`. (SLS
> 3.2.10)
>               new
> java.util.ArrayList[String]().stream.map(_.toInt).map(_.toString):
> JStream[String]
>                                                        ^
> <console>:9: error: type mismatch;
>  found   : java.util.function.Function[String,Int] with Serializable
>  required: java.util.function.Function[_ >: String, _ <: R]
>               new
> java.util.ArrayList[String]().stream.map(_.toInt).map(_.toString):
> JStream[String]
>
>
> W dniu sobota, 27 czerwca 2015 03:37:48 UTC+2 użytkownik Stephen Compall
> napisał:
>>
>>  On Fri, 2015-06-26 at 18:05 -0700, Roman Janusz wrote:
>>
>> Is there any chance this will work?
>>
>>  $ scala -Xexperimental
>> Welcome to Scala version 2.11.6 (Java HotSpot(TM) 64-Bit Server VM, Java
>> 1.8.0_40).
>> Type in expressions to have them evaluated.
>> Type :help for more information.
>>
>> scala> new java.util.ArrayList[String]().stream.map(_.toInt)
>> <console>:8: error: no type parameters for method map: (x$1: java.util.
>> function.Function[_ >: String, _ <: R])java.util.stream.Stream[R] exist
>> so that it can be applied to arguments (java.util.function.Function[
>> String,Int] with Serializable)
>>  --- because ---
>> argument expression's type is not compatible with formal parameter type;
>>  found   : java.util.function.Function[String,Int] with Serializable
>>  required: java.util.function.Function[_ >: String, _ <: ?R]
>>
>>
>> Not fatal, I would say.
>>
>> Welcome to Scala version 2.11.7 (OpenJDK 64-Bit Server VM, Java 1.8.0_45).
>> Type in expressions to have them evaluated.
>> Type :help for more information.
>>
>> scala> import java.util.ArrayList, java.util.stream.{Stream => JStream}
>> import java.util.ArrayList
>> import java.util.stream.{Stream=>JStream}
>>
>> scala> new java.util.ArrayList[String]().stream.map[Int](_.toInt)
>> res1: java.util.stream.Stream[Int] = java.util.stream.ReferencePipeline$3...@5b49c202
>>
>> scala> new java.util.ArrayList[String]().stream.map(_.toInt): JStream[Int]
>> res2: java.util.stream.Stream[Int] = java.util.stream.ReferencePipeline$3...@47bded3c
>>
>>
>> Not ideal, but maybe something else is going on here.
>>
>>   --
>> Stephen Compall
>> "^aCollection allSatisfy: [:each|aCondition]": less is better
>>
>>    --
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