Vritual extension methods

[Brian Goetz]

See the relevant section of State of the Lambda, 4th edition, which 
supersedes this.

On 7/4/2012 10:37 AM, Deepak S Patwardhan wrote:
> Hello,
>
>
>
> The Defender methods v4 document (Brian Goetz, June 2011) has two
> interesting foot notes (page 2)
>
>
>
> 5. It is a deliberate choice to not simply allow the programmer to include
> the code of the default inline
>
> within the interface. Among other reasons, it would violate the long-held
> rule that "interfaces don't have
>
> code".
>
>
>
> 6. The syntax of specifying the default implementation should match that of
> specifying method references, if
>
> method references are to be added to the language.
>
>
>
> Consider the following code (which compiles successfully with build 39)
>
>
>
> /* Complex.java */
>
> /** Represents Complex numbers */
>
> public interface Complex {
>
>
>
>      public Complex add(Complex b);
>
>
>
>      public Complex negate();
>
>
>
>      public Complex subtract(Complex b) default {
>
>          return this.add(b.negate());
>
>      }
>
>
>
>      public Complex multiply(Complex b);
>
>
>
>      public Complex invert();
>
>
>
>      public Complex divide(Complex b) default Complexes.divide;
>
> }
>
>
>
> /* Complexes.java */
>
> public class Complexes {
>
>
>
>      public static Complex divide(Complex a, Complex b) {
>
>          return a.multiply(b.invert());
>
>      }
>
>
>
> }
>
>
>
> First Question:
>
> As I am able to write a method body for subtract, the rule mentioned in
> footnote 5, interfaces don't have code, seems to have been ignored. Has this
> been finalized or will this be disallowed in a future build ?
>
>
>
> Second Question:
>
> Consider the default clause of the divide method. The syntax used for the
> method reference is ClassName.methodName. In section 8 of State of Lambda v4
> (Brian Goetz, December 2011), method references have syntax
> ClassName::methodName. It also states that this syntax is provisional.
> Example, map method of Iterable takes method references in this syntax.
>
>
>
> List<String> names = .
>
> nameLengths = names.map(String::length);
>
>
>
> Will the syntax for specifying the default method change to (only) use
> ClassName::methodName, in a future build ? Otherwise, footnote 6 also seems
> to be ignored for now.
>
>
>
> Regards,
>
> Deepak S Patwardhan.
>
>
>
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>