Fun with method references

[Rémi Forax]

Le 05/08/2010 15:54, John Nilsson a écrit :
> On Wed, Aug 4, 2010 at 11:33 PM, Brian Goetz<brian.goetz at oracle.com>  wrote:
>    
>> Check this out -- this works with the latest prototype:
>> Arrays.sortBy(foos, Foo#getA);          // sort by JavaBean property A
>>      
> I'm wondering if this kind of thing will increase the demand for
> tuples in the language. So far it has been my experience that most
> uses of classes such as Pair<A,B>  is better served by actually naming
> the attribute collection to something sensible. But with code like
> this I can see how a simple tuple would simplify things.
>
> So will
> Arrays.sortBy(foos, tuple(Foo#getA,Foo#getB))
> be good enough or would it be better with
> Arrays.sortBy(foos, (Foo#getA,Foo#getB)) // Standard parenthesis tuple syntax
> or
> Arrays.sortBy(foos, Foo#getA x Foo#getB) // Product combinator operator
>
> BR,
> John
>    

John,
my advice here is to use the varargs syntax (with an 
@SuppressWarnings("varargs"))
But it doesn't work with the current prototype.
Worst there is not lambda conversion between #int(String) and 
Extractor<?,? super K>.

import java.util.List;

public class MyTest2 {
   interface Extractor<U, T> {
    public U get(T t);
   }

   static class Arrays {
     public static <K extends Comparable<K>> void sortBy(List<K> c,  
Extractor<Integer,? super K> extractor) { }
     //public static <K extends Comparable<K>> void sortBy(List<K> c,  
Extractor<?,? super K> extractor) { }
     //public static <K extends Comparable<K>> void sortBy(List<K> c,  
Extractor<?,? super K>... extractor) { }
   }

   public static void main(String[] args) {
     List<String> list = java.util.Arrays.asList(args);
     Arrays.sortBy(list, #(String s){s.length()});
   }
}

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