Re: Unexpected compile error with reflective calls

On Mon, Mar 2, 2015 at 2:59 PM, Steven Heidel <[email protected]>
wrote:

> Take a look at the following code:
>
> import scala.language.reflectiveCalls
>
> trait A {
>   def sameName: Object
> }
>
> object B extends A {
>   def sameName = new Object {
>     def method = ???
>   }
>
>   def differentName = new Object {
>     def method = ???
>   }
>
>   def main = {
>     sameName.method // doesn't compile, "value call is not a member of
> Object"
>     differentName.method // compiles
>   }
> }
>
> I expected this to compile because I'm refining both the method sameName
> and differentName's Object with "method". The only difference is that
> sameName implements a method in trait A whereas differentName does not.
>
> I'm assuming this is because type inference picks up Object for the return
> type of sameName from trait A instead of its actual type Object{def method:
> Nothing}. Is this a bug or a feature?
>

Hi Steven,

This is intentional, albeit subtle.

The type of the overridden method A#sameName is used as the expected type
<https://github.com/scala/scala/blob/v2.11.5/src/compiler/scala/tools/nsc/typechecker/Namers.scala#L1099-L1111>
when typechecking the body of B#sameName. Furthermore, when typechecking an
instantiation of an anonymous class, the expected type is a signal to hide
declarations from the anonymous class
<https://github.com/scala/scala/blob/v2.11.5/src/compiler/scala/tools/nsc/typechecker/Typers.scala#L2309-L2353>
from the expression’s type.

If you don’t want to remember these rules (who would!?), annotating return
types of non-private methods is your best bet.
​
-jason

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