Noncopyable types cannot be conditionally cast

Using Swift
1

I would like to be able to cast non-copyables:

protocol P: ~Copyable {}

func castP<
    From: P & ~Copyable,
    To: P & ~Copyable
>(
    to _: To.Type = To.self,
    _ value: consuming From
) -> To? {
    value as? To // error: Noncopyable types cannot be conditionally cast
}

I see this topic from a year ago: Impossible to type cast or test non-copyable existential types?

It seems this wasn’t resolved at the time. Are there any plans to address it in the near future?

Any possible workaround to cast such values?

2

Just to note - I found a bit dirty workaround that seems to be working properly for my cases:

private final class _SafeNonCopyableCast<T: ~Copyable> {
    var value: T?

    init(_ value: consuming T) {
        self.value = .init(value)
    }

    consuming func `as`<To: ~Copyable>(_: To.Type) -> To? {
        let casted = self as? _SafeNonCopyableCast<To>
        return casted?.value.take()
    }
}

private func safeNonCopyableCast<
    From: P & ~Copyable,
    To: P & ~Copyable
>(
    _ from: consuming From,
    to: To.Type = To.self
) -> To? {
    _SafeNonCopyableCast(from).as(To.self)
}

I don't think it will work for all the types but works for the same type at least.

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