Add orEmpty extensions for immutable collections

Author: Goooler

core/api/kotlinx-collections-immutable.api

@@ -27,6 +27,9 @@ public final class kotlinx/collections/immutable/ExtensionsKt {
 	public static final fun mutate (Lkotlinx/collections/immutable/PersistentList;Lkotlin/jvm/functions/Function1;)Lkotlinx/collections/immutable/PersistentList;
 	public static final fun mutate (Lkotlinx/collections/immutable/PersistentMap;Lkotlin/jvm/functions/Function1;)Lkotlinx/collections/immutable/PersistentMap;
 	public static final fun mutate (Lkotlinx/collections/immutable/PersistentSet;Lkotlin/jvm/functions/Function1;)Lkotlinx/collections/immutable/PersistentSet;
+	public static final fun orEmpty (Lkotlinx/collections/immutable/ImmutableList;)Lkotlinx/collections/immutable/ImmutableList;
+	public static final fun orEmpty (Lkotlinx/collections/immutable/ImmutableMap;)Lkotlinx/collections/immutable/ImmutableMap;
+	public static final fun orEmpty (Lkotlinx/collections/immutable/ImmutableSet;)Lkotlinx/collections/immutable/ImmutableSet;
 	public static final fun persistentHashMapOf ()Lkotlinx/collections/immutable/PersistentMap;
 	public static final fun persistentHashMapOf ([Lkotlin/Pair;)Lkotlinx/collections/immutable/PersistentMap;
 	public static final fun persistentHashSetOf ()Lkotlinx/collections/immutable/PersistentSet;

core/commonMain/src/extensions.kt

@@ -30,6 +30,11 @@ import kotlinx.collections.immutable.implementations.persistentOrderedSet.Persis
  */
 public inline fun <T> PersistentSet<T>.mutate(mutator: (MutableSet<T>) -> Unit): PersistentSet<T> = builder().apply(mutator).build()
 
+/**
+ * Returns this [ImmutableSet] if it's not `null` and the empty [ImmutableSet] otherwise.
+ */
+public inline fun <T> ImmutableSet<T>?.orEmpty(): ImmutableSet<T> = this ?: persistentSetOf()
+
 /**
  * Returns the result of applying the provided modifications on this list.
  *
@@ -52,6 +57,10 @@ public inline fun <T> PersistentList<T>.mutate(mutator: (MutableList<T>) -> Unit
 public inline fun <K, V> PersistentMap<out K, V>.mutate(mutator: (MutableMap<K, V>) -> Unit): PersistentMap<K, V> =
         (this as PersistentMap<K, V>).builder().apply(mutator).build()
 
+/**
+ * Returns this [ImmutableList] if it's not `null` and the empty [ImmutableList] otherwise.
+ */
+public inline fun <T> ImmutableList<T>?.orEmpty(): ImmutableList<T> = this ?: persistentListOf()
 
 /**
  * Returns the result of adding the specified [element] to this collection.
@@ -440,6 +449,10 @@ public operator fun <K, V> PersistentMap<out K, V>.minus(keys: Array<out K>): Pe
 public operator fun <K, V> PersistentMap<out K, V>.minus(keys: Sequence<K>): PersistentMap<K, V>
         = mutate { it.minusAssign(keys) }
 
+/**
+ * Returns the [ImmutableMap] if it's not `null`, or the empty [ImmutableMap] otherwise.
+ */
+public fun <K, V> ImmutableMap<K, V>?.orEmpty(): ImmutableMap<K, V> = this ?: persistentMapOf()
 
 /**
  * Returns a new persistent list of the specified elements.

core/commonTest/src/contract/list/ImmutableListTest.kt

@@ -224,4 +224,12 @@ class ImmutableListTest {
 
         assertEquals<List<*>>(listOf("x", null, 1), listAny)
     }
+
+    @Test fun immutableListOrEmpty() {
+        val emptyList = (null as ImmutableList<String>?).orEmpty()
+        val notEmptyList = persistentListOf("a")
+
+        assertEquals(emptyList, persistentListOf())
+        assertEquals(notEmptyList, notEmptyList.orEmpty())
+    }
 }

core/commonTest/src/contract/map/ImmutableMapTest.kt

@@ -392,4 +392,13 @@ abstract class ImmutableMapTest {
 
         testEquality(data, changed)
     }
+
+    @Test
+    fun immutableMapOrEmpty() {
+        val emptyMap = (null as PersistentMap<String, Int>?).orEmpty()
+        val notEmptyMap = persistentMapOf("a" to 1)
+
+        assertEquals(emptyMap, persistentMapOf())
+        assertEquals(notEmptyMap, notEmptyMap.orEmpty())
+    }
 }

core/commonTest/src/contract/set/ImmutableSetTest.kt

@@ -404,4 +404,13 @@ abstract class ImmutableSetTestBase {
 
         testEquality(data, changed)
     }
+
+    @Test
+    fun immutableSetOrEmpty() {
+        val emptySet = (null as ImmutableSet<String>?).orEmpty()
+        val notEmptySet = persistentSetOf("a")
+
+        assertEquals(emptySet, persistentSetOf())
+        assertEquals(notEmptySet, notEmptySet.orEmpty())
+    }
 }