How to filter results of a virtual method?

[Jim Laskey]

I think it's a simple issue.  Drop should use 1 instead of 0.


    public static
    MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
        MethodType targetType = target.type();
        MethodType filterType = filter.type();
        if (filterType.parameterCount() != 1
            || filterType.parameterType(0) != targetType.returnType())
            System.err.println("target and filter types do not match");
        // FIXME: Too many nodes here.
        MethodHandle returner = dropArguments(filter, 0, targetType.parameterList());   <<<  0 should be 1
        return foldArguments(returner, exactInvoker(target.type()).bindTo(target));
    }

Cheers,

-- Jim





On 2011-01-26, at 1:17 PM, Jim Laskey wrote:

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> 
> 
> Is there a way to filter the result of a virtual method?  Seems okay for statics, but receiver runs interference on virtual calls.
> 
> Running the enclosed I get;
> 
> 10.0
> java.lang.IllegalArgumentException: target and combiner types must match: (TestFilter,int)double != (TestFilter)int
>        at sun.dyn.MemberName.newIllegalArgumentException(MemberName.java:513)
>        at java.dyn.MethodHandles.misMatchedTypes(MethodHandles.java:1706)
>        at java.dyn.MethodHandles.foldArguments(MethodHandles.java:1646)
>        at java.dyn.MethodHandles.filterReturnValue(MethodHandles.java:1588)
>        at TestFilter.main(TestFilter.java:29)
> 
> 
> Source:;
> 
> import java.dyn.*;
> 
> public class TestFilter {
> 
>    public static int a = 10;
>    public int b = 10;
> 
>    public static double filter(int x) {
>        return (double)x;
>    }
> 
>    public static void main(String[] args) {
>        try {
>            MethodHandles.Lookup lookup = MethodHandles.lookup();
>            MethodHandle getter = lookup.findStaticGetter(TestFilter.class, "a", int.class);
>            MethodHandle filter = lookup.findStatic(TestFilter.class, "filter", MethodType.methodType(double.class, int.class));
>            MethodHandle filteredGetter = MethodHandles.filterReturnValue(getter, filter);
> 
>            Object result = filteredGetter.invokeWithArguments();
>            System.out.println(result);
>        } catch (Throwable throwable) {
>            throwable.printStackTrace();
>        }
> 
>        try {
>            MethodHandles.Lookup lookup = MethodHandles.lookup();
>            MethodHandle getter = lookup.findGetter(TestFilter.class, "b", int.class);
>            MethodHandle filter = lookup.findStatic(TestFilter.class, "filter", MethodType.methodType(double.class, int.class));
>            MethodHandle filteredGetter = MethodHandles.filterReturnValue(getter, filter);
> 
>            TestFilter m = new TestFilter();
>            Object result = filteredGetter.invokeWithArguments();
>            System.out.println(result);
>        } catch (Throwable throwable) {
>            throwable.printStackTrace();
>        }
>    }
> }
>