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Data Structure Maps

FastMap, IntMap, IntIntMap, IntFloatMap, CacheMap, CaseInsensitiveStringMap, WeakMap, MapList extensions...

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FastMap: FastIntMap, FastStringMap

Simpler Map-like structures that uses native specific implementations to improve performance and reduce allocations.

val map = FastIntMap<String>()
assertEquals(0, map.size)
map[1] = "a"
map[2] = "b"
assertEquals(listOf(1, 2), map.keys.sorted())
assertEquals(2, map.size)
assertEquals("a", map[1])
assertEquals("b", map[2])
assertEquals(null, map[3])

IntMap: IntMap, IntIntMap, IntFloatMap

Variants of a hashmap implementation using int as keys without boxing (and Object, int or float for values). The implementation requires just a couple of arrays for working (no nodes at all). It uses a multihash approach for filling as much as possible with a logarithmic stash. Just allocates when growing.

val m = IntIntMap()
m[0] = 98
assertEquals(1, m.size)
assertEquals(98, m[0])
assertEquals(0, m[1])


Works like a LinkedHashMap with a limited amount of elements. When inserting new elements after reaching the maximum amount of elements, the oldest element inserted is deleted.

val cache = CacheMap<String, Int>(maxSize = 2)
cache["a"] = 1
cache["b"] = 2
cache["c"] = 3
assertEquals("{b=2, c=3}", cache.toString())


Map with String keys considered case insensitive. Case of the original keys is preserved, but keys can be accessed with any case.

val map = CaseInsensitiveStringMap("hELLo" to 1, "World" to 2)
assertEquals(2, map.size)
assertEquals(1, map["hello"])
assertEquals(2, map["world"])

It is possible to convert a normal Map<String, *> to a CaseInsensitive one with the toCaseInsensitiveMap extension:

val map = mapOf("hELLo" to 1, "World" to 2).toCaseInsensitiveMap()


Provides a WeakMap data structure that internally uses JS’s WeakMap, JVM’s WeakHashMap and Native’s WeakReference. WeakProperty allow to define external/extrinsic properties to objects that are collected once the object is not referenced anymore.

val map = WeakMap<Demo, String>()
val demo1 = Demo()
map[demo1] = "hello"

assertEquals("hello", map[demo1])

Note that using this primitive on JavaScript requires ES6 support (and it doesn’t work on IE10 or lower). Check the JS’s WeakMap compatibility table for more information.

MapList extensions

Instead of providing a MutableMap<K, MutableList<V>> implementation. Kds provides a set of methods and extension methods to easily work with those kind of maps.

val map = linkedHashMapListOf("a" to 10, "a" to 20, "b" to 30)

assertEquals(10, map.getFirst("a"))
assertEquals(20, map.getLast("a"))

assertEquals(30, map.getFirst("b"))
assertEquals(30, map.getLast("b"))

assertEquals(null, map.getLast("c"))

assertEquals(listOf("a" to 10, "a" to 20, "b" to 30), map.flatten())
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