Feedback and comments on ARM proposal

[Joshua Bloch]

Mark,

On Sat, Mar 21, 2009 at 9:37 AM, Mark Mahieu <markmahieu at googlemail.com>wrote:

> Hi Josh,
>
> 2009/3/21 Joshua Bloch <jjb at google.com>
>
>> What if you have an interface that extends an interface that extends the
>> magic marker?  There should be nothing wrong with that.  While there may be
>> some easy way to specify this (and give it reasonable semantics) it isn't
>> jumping out at me.  If anyone has any clever ideas along these lines, I'd
>> love to know.
>>
>
> I'm probably missing the point, but doesn't the JLS generally use the
> phrase 'is a subtype of' to describe this kind of relationship?
>

 I don't think I did a good job of explaining the problem. Consider this:

interface Closeable extends MagicMarker {
    void close();
}

interface Foo extends Closeable { // Must be OK for ARM
    // Lots of methods
}

class bar implements Foo { // Must be OK for ARM
    // Lots of methods
}

interface Baz extends Foo { //
  // No new methods
}

class Qux Implements Foo, Baz { // Probably OK for Arm
]

interface Disposable extends MagicMarker {
    public void dispose();
}

class Nope implements Closeable, Disposeable {  // Probably not OK for ARM
}

The problem with Nope is that it contains two "magic methods"  (sole
parameterless method in an interface that directly extends MagicMarker).  Is
it sufficient to say that a class must have one and only one magic method to
make it eligible for automatic resource management?  Is it practical to
implement this in the compiler? I dunno.

         Josh

          Josh