MethodHandle for array length

[Michael Haupt]

Hi Uwe,

> Am 11.05.2016 um 21:35 schrieb Uwe Schindler <uschindler at apache.org>:
> With Java 9 this gets a bit worse: There is no "easy way" with the MethodHanldes class to generate a MethodHandles.countedLoop() on all elements of an array:
> 
> public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle  body) [new in Java 9]

this isn't a remedy when you need the index in each iteration, but you can generate a loop over all elements of an array using iteratedLoop(), as illustrated by this test from LoopCombinatorTest:

@Test
public static void testIterateSum() throws Throwable {
    // Integer[] a = new Integer[]{1,2,3,4,5,6}; int sum = 0; for (int e : a) { sum += e; } return sum; => 21
    MethodHandle loop = MethodHandles.iteratedLoop(Iterate.MH_sumIterator, Iterate.MH_sumInit, Iterate.MH_sumStep);
    assertEquals(Iterate.MT_sum, loop.type());
    assertEquals(21, loop.invoke(new Integer[]{1, 2, 3, 4, 5, 6}));
}

... where MH_sumIterator is a handle to this method:

static Iterator<Integer> sumIterator(Integer[] a) {
    return Arrays.asList(a).iterator();
}

Best,

Michael

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