Enhanced Enums -- use cases

[Vicente Romero]

Hi,

Some additional examples, this one shows code sharing between enum constants

public class SharingCodeWithEnhancedEnums {
     enum Primitive<X> {
         INT {
             // instead of replicating code INT.even() can make use of 
LONG.even()
             boolean even(int value) { return LONG.even(value); }
         },
         LONG {
             boolean even(long value) { return value % 2 == 0; }
         };
     }

     public static void main(String... args) {
         // prints: true
         System.out.println(Primitive.INT.even(4));
     }
}

This one shows the power of sharper typing

enum EnumConstants {
     BYTE {
         static final int BITSIZE = 8;
     },
     INT {
         static final int BITSIZE = 32;
     };

     public static void main(String... av) {
         System.out.println("BYTE.BITSIZE = " + BYTE.BITSIZE); // 
prints: BYTE.BITSIZE = 8
         System.out.println("INT.BITSIZE = " + INT.BITSIZE);   // 
prints: INT.BITSIZE = 32
     }
}

Thanks,
Vicente

On 04/11/2017 03:11 PM, Brian Goetz wrote:
> As you may have noticed, we pushed an implementation of Enhanced Enums 
> some time ago.  We're hoping to get user feedback on the feature as it 
> is now implemented.
>
> To get things started, here are some typical use cases where generic 
> enums might be useful.  Please contribute others, as well as places in 
> the JDK where code could be refactored using this feature.
>
> An obvious example is com.sun.tools.javac.code.Dynamic 
> (http://hg.openjdk.java.net/valhalla/valhalla/langtools/file/85cc92a65da8/src/jdk.compiler/share/classes/com/sun/tools/javac/code/Dynamic.java#l51), 
> where we have an enum that represents the kinds of types representable 
> in the constant pool.
>
> In that case, these factory methods:
>
> http://hg.openjdk.java.net/valhalla/valhalla/langtools/file/85cc92a65da8/src/jdk.compiler/share/classes/com/sun/tools/javac/code/Dynamic.java#l137 
>
>
> should be collapsible to a single generic method:
>
>     <D> static BootstrapArgument<D> constant(Kind<D> kind, D data).
>
>
> Another example is command line parsing; for command line arguments, 
> we can represent them as enums whose type represents the type of an 
> (optional) parameter:
>
>     enum Args {
>         QUIET<??>("quiet", "q"),
>         FILE<String>("file", "f"),
>         COUNT<Integer>("count", "c"), ....
>     }
>
> (though its not obvious what the type arg of QUIET should be.)
>
>
> If anyone wants to experiment and offer their experience in applying 
> (or misapplying) this feature, either to the JDK or their own 
> codebase, that would be appreciated....
>
>