Kotlin: Intersect maps with different value types on their keys

KotlinMapIntersection.kt

/**
 * Intersect two maps with same keys, but different data types. Preserves the order of the first map.
 * Returns a list of the combined type provided by the transformation.
 */
inline fun <Key, Value1, Value2, T> Map<Key, Value1>.intersectWith(
        other: Map<Key, Value2>,
        transformationFunction: (Value1, Value2) -> T): List<T> {
    return flatMap { oldEntry ->
        other.filterKeys { it == oldEntry.key }
                .map { transformationFunction(oldEntry.value, it.value) }
    }
}

/**
 * Intersect two maps with same keys, but different data types. Preserves the order of the first map.
 * Returns a list of pairs of both value types.
 */
fun <Key, Value1, Value2> Map<Key, Value1>.intersectWith(other: Map<Key, Value2>): List<Pair<Value1, Value2>> {
    return flatMap { oldEntry ->
        other.filterKeys { it == oldEntry.key }
                .map { Pair(oldEntry.value, it.value) }
    }
}