jackson-databind

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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()

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).

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

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