Confused by https://issues.scala-lang.org/browse/SI-490

On 6/27/11 1:17 AM, Chris Marshall wrote:
> This looks to me like a complete break with the behaviour I would
> expect. That is, the result of calling a method on some instance "a"
> depends on the static type of a's reference - completely at odds with
> how other "instance" methods work.

The result doesn't depend on it: all those examples return the same value. The type of the result does. What are these other "instance" methods? newInstance is a method on Class.

It's the same in java.

http://download.oracle.com/javase/6/docs/api/java/lang/Object.html#getCl...

"The actual result type is Class<? extends |X|> where |X| is the erasure of the static type of the expression on which getClass is called."

On Mon, Jun 27, 2011 at 10:17 AM, Chris Marshall <oxbow_lakes@hotmail.com> wrote:

Am I missing something?

yes, the static-dynamic divide:  
statically, `x.getClass().newInstance()` has type `T` if `x` has type `T`
the runtime behaviour is illustrated below:

Welcome to Scala version 2.10.0.r25149-b20110624145919 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_24).Type in expressions to have them evaluated.Type :help for more information.
scala>  class Adefined class A
scala>  class B extends Adefined class B
scala> def f3 = (new B: A).getClass().newInstance() f3: A
scala>  (new B: A).getClass()res0: java.lang.Class[_ <: A] = class B
scala> res0.newInstance()res1: A = B@501d5ebc

Apologies - I thought that you were indicating the type of object created, as opposed to the type of its reference. 
By "instance" method, I meant "a method which is not a static method" - old terminology I think I was first indoctrinated with when being taught Smalltalk (except a "static" method would have been called a "class" method in Smalltalk).

Chris
> Date: Mon, 27 Jun 2011 01:27:51 -0700
> From: paulp@improving.org
> To: scala-internals@googlegroups.com
> CC: oxbow_lakes@hotmail.com
> Subject: Re: [scala-internals] Confused by https://issues.scala-lang.org/browse/SI-490
>
> On 6/27/11 1:17 AM, Chris Marshall wrote:
> > This looks to me like a complete break with the behaviour I would
> > expect. That is, the result of calling a method on some instance "a"
> > depends on the static type of a's reference - completely at odds with
> > how other "instance" methods work.
>
> The result doesn't depend on it: all those examples return the same value. The type of the result does. What are these other "instance" methods? newInstance is a method on Class.
>
> It's the same in java.
>
> http://download.oracle.com/javase/6/docs/api/java/lang/Object.html#getCl...
>
> "The actual result type is Class<? extends |X|> where |X| is the erasure of the static type of the expression on which getClass is called."

On 6/27/11 1:43 AM, Chris Marshall wrote:
> By "instance" method, I meant "a method which is not a static method" -

Oh, those are called instance methods.