Question on layer/peeling

[Brian Goetz]

Yes, this is pretty straightforward.  In the bucket of "things that are 
easy and small, so we'll ignore them until we solve the ones that are 
big and difficult.")

The hardest part is picking a syntax (please, no suggestions!)


On 1/5/2015 9:19 PM, Vitaly Davidovich wrote:
> C# has a default (T) keyword to allow generic code to obtain the "zero"
> value for a type param.  Something like that for java would be nice.
>
> Sent from my phone
> On Jan 5, 2015 9:15 PM, "Michael Barker" <mikeb01 at gmail.com> wrote:
>
>> Hi,
>>
>> The SotS talks about the use of 'layer' to create an alternative
>> implementation of methods when the type of an <any T> is known to be a
>> reference type.  However, the examples only show the use of the layer
>> keyword on an interface definition, where as I've encountered at least one
>> case where the internal implementation needs to differentiate between a
>> reference-type and value-type based collection.  The example I'm thinking
>> about is the null-ing out of array elements in a collection (which is
>> obviously a no-op with a value type, but necessity with reference
>> types).  Is an interface required in order to define a 'layer' or could it
>> be done within a concrete class?
>>
>> E.g. is the following or something similar possible?  If not, how would it
>> be achieved with current spec?
>>
>> class ArrayList<any T> {
>>      T[] values;
>>      int position;
>>
>>      void removeLast() {
>>          if (position <= 0) {
>>              return;
>>          }
>>
>>          --position;
>>          clear(position);
>>      }
>>
>>      private void clear(int index) {
>>      }
>>
>>      layer<ref T> {
>>          private void clear(int index) {
>>              values[index] = null;
>>          }
>>      }
>> }
>>
>> Mike.
>>