Wanted: overloading use cases

Dan Smith daniel.smith at oracle.com
Wed Oct 10 16:23:26 PDT 2012

On Oct 10, 2012, at 5:07 PM, Remi Forax <forax at univ-mlv.fr> wrote:

> On 10/11/2012 12:48 AM, Dan Smith wrote:
>> I've recently been exploring and refining our overload resolution algorithm for Lambda.  I'm looking for some real-world examples of Lambda code that we should support.  If you have experience with a library that makes use of lambda-like features (in any language, or a Java library that could naturally be enhanced with lambda support), please read on!
>> A typical challenging use case for overload resolution looks like this:
>> interface Stream<E> {
>>  <R> Stream<R> map(Mapper<E, R> m);
>>  IntStream map(IntMapper<E> m);
>>  LongStream map(LongMapper<E> m);
>> }
>> Stream<Foo> s = ...;
>> s.map(f -> f.method());
> I hope this example calls map(IntMapper).

Depends on the declaration of 'Foo'. :-)

Yes, if the lambda body produces an int (or short, or byte) the IntMapper one would be preferred over the other two.

>> Notable properties of this example:
>> 1) There are multiple methods of the same arity, differing in a functional interface parameter type
>> 2) The arities of the corresponding functional interfaces are identical
>> 3) No non-lambda argument can be used for disambiguation
>> 4) The functional interfaces have the same parameter type(s)
> I don't understand, 1 and 4 are contradictory, no ?

Yes, I was a bit unclear.  The _overloaded methods_ have different parameter types (e.g., IntMapper vs. LongMapper).  The _functional interface methods_ have the same parameter types (e.g., E).

(1) might have been better stated as "differing in a parameter type that is a different functional interface for each method", or something like that.


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