WreckedCast.java

public class WreckedCast {

    @SuppressWarnings("unchecked")
    static <P, PP extends Parametric<P>> PP wreckedCast(Parametric<? extends Parametric<P>> ppp) {
        return (PP) ppp.extract();
    }

    public static void main(String[] args) {
        // java.lang.ClassCastException: WreckedCast$Parametric$$Lambda$1/1607521710 cannot be cast to java.lang.String
        System.out.println(wreckedCast(Parametric.parametric(Parametric.parametric(1))));

        //this doesn't help
        System.out.println(wreckedCast(Parametric.<Parametric<Integer>>parametric(Parametric.parametric(1))));

        //not even this helps
        Parametric<Parametric<Integer>> parametric = Parametric.parametric(Parametric.parametric(1));
        System.out.println(wreckedCast(parametric));

        Parametric<Integer> onlyWorksIfExplicitlyTyped = wreckedCast(Parametric.parametric(Parametric.parametric(1)));
        System.out.println(onlyWorksIfExplicitlyTyped);

        /*
        For some reason I'm not yet sure of, javac is determining that the appropriate println() overload to dispatch
        to is println(String), rather than println(Object), even though, regardless of what Parametric is, it can't
        possibly be a String.

        Thus, the resulting bytecode is generated:

        CHECKCAST java/lang/String
        INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V

        Naturally, the CHECKCAST blows up.

        Interestingly, changing wreckedCast's argument's covariant bound on Parametric<P> to be invariant, resulting
        in the argument Parametric<Parametric<P>>, also resolves this.
        */
    }

    public interface Parametric<P> {
        P extract();

        static <P> Parametric<P> parametric(P p) {
            return () -> p;
        }
    }
}