extension method implementations for methods of java.lang.Object

[Brian Goetz]

But, even given that, in this case the resolution for a call to equals() would 
go straight to Object.equals(), since we only consult defaults if the object 
does not already have an implementation from its inheritance hierarchy.  All 
objects already have an equals().

On 8/19/2010 4:50 AM, Maurizio Cimadamore wrote:
> On 19/08/10 08:59, Thomas Jung wrote:
>> Hi,
>>
>> with the current prototype it's not possible to define a default
>> implementation for Object#equals.
>>
>> interface A{
>> 	extension boolean xequals(Object obj) default As.eq;
>> 	extension boolean equals(Object obj) default As.eq;
>> }
>>
>> static class As{
>> 	public static boolean eq(A me, Object object){
>> 		throw new RuntimeException();
>> 	}
>> }
>>
>> a.equals(new Object());    //passes
>> a.xequals(new Object());  //throws exception
>>
>> This feature is useful if the equals implementation for some subtypes
>> of A can be expressed based on the methods defined in A.
>>
> The VM extension required to handle extension methods at runtime is not
> available yet - as a result it is not possible to get to execute the
> above code (or any code containing extension methods) with the right
> semantics... in fact, since the runtime infrastructure is missing, the
> VM gets method dispatching completely wrong - the invokevirtual
> targeting A.equals() is dispatched to Object.equals() while for
> A.xequals() the VM complains because it cannot find a suitable
> implementation of xequals() inside the instance 'a'.
>
> Maurizio
>>    -
>> Thomas
>>
>>
>
>