Re: Improved for each loop

From:
Joshua Cranmer <Pidgeot18@verizon.invalid>
Newsgroups:
comp.lang.java.programmer
Date:
Mon, 13 Jul 2009 17:17:14 -0400
Message-ID:
<h3g88t$23b$1@news-int.gatech.edu>
markspace wrote:

The difference between this and the regular for-each is that the
identifier after the colon isn't an object (not an Iterable or an array)
but an integer primitive. It should work even with literals:

  for( int i : 42 ) {
    .... // i == 0..41 inclusive
  }


The problem here is that the syntax is slightly ambiguous on read: does
i achieve the value of 42 or not?

If you really want this feature, it's possibly right now:

public final class IteratorUtils {
   public static <T> Iterable<T> getIterable(final Iterator<T> it) {
     return new Iterable<T>(){public Iterator<T> iterator(){return it;}};
   }
   public static Iterable<Integer> range(final int high) {
     return getIterable(new Iterator<Integer>() {
       private int i = 0;
       public boolean hasNext() { return i == high; }
       public Integer next() { return i++; }
       public void remove() {}
     });
   }

   public static void main(String... args) {
     for (int i : range(42)) {
       System.out.println(i);
     }
   }
}

With Java 7 coming up, is this JSR worthy?


I believe you're looking for Project Coin (a collection of small
language changes for JDK 7), but its ultimate acceptance would be
suspect: the ability to create one's own Iterable implementations means
that it's almost trivial to roll it out, and probably easier to
understand that way, too.

--
Beware of bugs in the above code; I have only proved it correct, not
tried it. -- Donald E. Knuth

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