> if an entry isn’t in the base map, it won’t ...

# codereview

[kingsley]

if an entry isn’t in the base map, it won’t exist in the final one

Yes. Which is why I iterated through mapOverride instead. This is a union of both maps with the assumption that they only contain sets/other values and a key always points to values of similar type (or null) in both maps. Entries in mapOverride are always preferred except for sets where both will get merged

I suppose that is what you’re trying to achieve?

[dave08]

Exactly.

[dave08]

I have one more type to add here: Map<String, Set<String>>... and all these erased types makes it more complicated than it should be...

[dave08]

The original is from a json document that has "common" and "conditional" keys and each of them is an object that has a { key -> one of the three types, ... }. conditional needs to be merged over common.

[kingsley]

I have one more type to add here: Map<String, Set<String>>

You mean this as input? The mergeWith will handle it as well

[kingsley]

one of the three types

I’m assuming this is String, Set<String> and null? 🤔

[dave08]

Map<String, Map<String, Set<String>>>

[kingsley]

Aha. Okay

[kingsley]

What should happen in this case?

[dave08]

Any key that exists in override should just reset the set (not add to it...)

[dave08]

Like by the String type.

[dave08]

That's why I started with all those casts...

[kingsley]

This should do that:

fun MutableMap<String, Any>.mergeWith(mapOverride: Map<String, Any>?) {
    mapOverride?.forEach { (k, v) ->
        val baseValue = this[k]
        this[k] = when {
            baseValue is Set<*> && v is Set<*> -> baseValue + v
            baseValue is Map<*, *> && v is Map<*, *> -> baseValue + v
            else -> v
        }
    }
}

[kingsley]

You’d notice I used + in both cases. That’s fine, since the operands are of different types, the operator resolves to different methods, as it applies to Set and Map accordingly

[dave08]

Cool! But then, when a key is in override that isn't in base...?

[kingsley]

…then it will add it to base

[dave08]

Very nice 😁, thanks alot!

[kingsley]

You’re welcome! 🙂