Add T[] Value.toJavaArray(T[])

[danieldietrich]

(See #1578)

These are our options:

// unsafe
T[] toJavaArray(Class<? super T> componentType) // one size fits all

vs

// safe
T[] toJavaArray(Class<T> componentType) // variant for non-generic types
T[] toJavaArray(T[] array)

I think the first, unsafe variant is no viable solution.

Example:

// before
Value<CharSequence> v = Option.of("");
CharSequence[] s = v.toJavaArray(CharSequence.class);

// after
Value<String> v = Option.of("");
String[] s = v.toJavaArray(CharSequence.class); // will eventually throw at runtime

The existing method toJavaArray(Class<T>) is still useful for non-generic types,
we do not need to deprecate it.

[l0rinc]

T[] toJavaArray(T[] array)

Because of erasure I don't think it's possible to make this completely type-safe.

I think the first, unsafe variant is no viable solution.

Doing it the Java way would result in the same unsafety

@SuppressWarnings("unchecked")
Option<Integer>[] options = singletonList(Option.some(1)).toArray(new Option[0]);
System.out.println(options[0].get());

i.e you cannot call toArray with new Option<Integer>[0] either ...

[danieldietrich]

@paplorinc you are right - it makes no sense to have toArray(T[]). That is the reason I introduced the simpler toArray(Class<T>).

If an application of toArray(Class<T>) compiles, it is correct. Therefore this is the best solution we can come up with.

For now, we will not implement the unsafe case, I don't see the urge to do it. We have many other things to do.

[l0rinc]

If an application of toArray(Class) compiles, it is correct.

Unfortunately that's not true either:

Array.of(1).toJavaArray(int.class);

errs at run time with:

java.lang.ClassCastException: [I cannot be cast to [Ljava.lang.Object;

I still think the <? super T> variant was the best compromise.

[danieldietrich]

I'm not sure. Is it possible to fix our variant, e.g. by first checking type.isPrimitive() and then decide further how to proceed?

I will play around a bit.

Safety first.

[l0rinc]

checking type.isPrimitive() and then decide further how to proceed?

and throw a different kind of RuntimeException?

Safety first.

I agree, but I don't think it's possible, because of type erasure, it's inherently unsafe :/

[danieldietrich]

See #1585