Add `JsonNode.map()` method

[cowtowncoder]

As a simple functional add-on, let's add something like this on JsonNode:

public <R> R map(Function<? super JsonNode, ? extends R> mapper);

[felldo]

If anyone else was wondering, this seems to be a breaking change when using Kotlin.

arrayNode.map { it.get("a").asString() }.distinct() // Works on <3.1.0
arrayNode.values().map { it.get("a").asString() }.distinct() // Workaround for >3.1.0

The new jackson map method takes precedence over Kotlin map function

[cowtowncoder]

@felldo That is unfortunate. Could you file an issue on https://github.com/FasterXML/jackson-module-kotlin ? Not sure what can be done, but at least raise awareness.

[k163377]

It may be a bit late to bring this up, but I find it a bit odd that this function is named map.
If it’s called map, shouldn’t the return type be JsonNode?

I’m not entirely sure if this is the best name, but I feel that something like materialize might be better.

[cowtowncoder]

It maps JsonNode into something else, not necessarily JsonNode. Limiting to JsonNode would make method much less useful.
I guess transform() could have qualified as a name but to me operation is mapping from one type to another, much like Optional.map() (but without wrapping).

And yes, unfortunately it is too late to rename (we could add new version but would need to retain old one as deprecated anyway).

[k163377]

to me operation is mapping from one type to another, much like Optional.map() (but without wrapping).

I don’t think a function named map should alter the type it wraps.
For example, Stream.map returns a Stream, and Optional.map returns an Optional.

As you say, I don’t think we should name operations that completely transform the type as map going forward.

And yes, unfortunately it is too late to rename (we could add new version but would need to retain old one as deprecated anyway).

So, does that mean we can’t remove it until Jackson 4.0?
Personally, I think we should deprecate it and add a function with a new name.

[cowtowncoder]

Right, cannot drop until 4.0.

And I don't see a reason to deprecate it at this point.

[rahulwermunddmde]

If anyone else was wondering, this seems to be a breaking change when using Kotlin.

arrayNode.map { it.get("a").asString() }.distinct() // Works on <3.1.0
arrayNode.values().map { it.get("a").asString() }.distinct() // Workaround for >3.1.0
The new jackson map method takes precedence over Kotlin map function

I'd say arrayNode.asIterable().map { ... } is a better workaround since it doesn't involve the creation of any new sequences. Cumbersome, nevertheless.