JsonNode#deepCopy ClassCast Exceptions

[D3v01dZA]

The current signature of JsonNode#deepCopy looks like this:

public abstract <T extends JsonNode> T deepCopy();

I wondered about the decision to do this as you can quite easily create a ClassCastException using this as follows:

TextNode text = TextNode.valueOf("SomeText"); ObjectNode object = text.deepCopy();

This code is obviously incorrect just by looking at it however this will always compile and throw an exception at runtime. I know this is considered an API change but a signature that prevents this might be:

JsonNode.java public abstract JsonNode deepCopy();

And then be overridden on each subclass with the correct type

ValueNode.java public abstract ValueNode deepCopy();

After looking at this again, the signatures of ObjectNode and ArrayNode are correct but you can still trick it by upcasting to JsonNode and then using deepCopy()

[cowtowncoder]

Hmmh. Yes, it would be possible to use return type co-variance here. This could be done for Jackson 3.x (as it can not be done for 2.x; not something that can go in a patch, and 2.9 is the last 2.x minor version).

[cowtowncoder]

lol on "2.9 is the last". We are at 2.13 now... :)

Still, if done, this needs to go in 3.0.