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Description
As per spec this is not currently supported.
But javac support them just fine and they are quite useful. The following program return true in Java:
import java.util.function.Function;
import java.util.function.Supplier;
@FunctionalInterface
public interface Maybe<A> {
<X> X fold(Supplier<X> empty, Function<A, X> just);
static <A, X> X empty0(Supplier<X> empty, Function<A, X> just) {
return empty.get();
}
static <A> Maybe<A> empty() {
return Maybe::empty0;
}
static void main(String[] args) {
Maybe<?> emptyString = Maybe.<String>empty();
Maybe<?> emptyInt = Maybe.<Integer>empty();
System.out.println(emptyString == emptyInt); // print "true".
}
}Fixing this issue would mean that the following code compile and print "true":
trait Maybe[A] {
def fold[X](empty: => X, just: A => X): X
}
object Maybe {
def empty0[A, X](empty: => X, just: A => X): X = empty
def empty[A]: Maybe[A] = empty0(_ , _) // does not compile
def main(args: Array[String]): Unit = {
val emptyString: Maybe[String] = Maybe.empty
val emptyInt: Maybe[Integer] = Maybe.empty
print(emptyString eq emptyInt) // how to make this print "true"???
}
}