What is the most efficient way to modify the value...

# announcements

[carbaj0]

What is the most efficient way to modify the values of an immutable Map<K,V> using is Key?

[diesieben07]

I assume you mean "make a new map", because obviously you can't modify an immutable map.
I would do

val newMap = map.toMutableMap()
newMap[key] = newValue

[carbaj0]

I was thinking of something like:

myMap.map {
    if(it.key == currentKey)
        //modify his values
    else 
        //return the original Map.Entry
}

[diesieben07]

That's less efficient most likely.

[carbaj0]

Thanks! i´m going to try your solution

[Ruckus]

val newMap = map + (key to value)

[carbaj0]

I was just creating this function:

[carbaj0]

fun <K, V> Map<K, V>.replace(key: K, values: V) =
    toMutableMap().apply { this[key] = values }

[carbaj0]

😅

[Michael Böiers]

Misleading, isn’t it? It suggests that it modifies the (immutable) map in place, but depending on what toMutableMap() does (or will do in the future), it might copy the data and return a new map (which is the current implementation). You could call it with or copy and make it return an immutable map again.

[carbaj0]

fun <K, V> Map<K, V>.copy(key: K, values: V): Map<K, V> =
    toMutableMap().apply { this[key] = values }

return an immutable map again explicitly it's really a good point