Use common atomics on non-JVM platforms

arrow-libs/core/arrow-atomic/build.gradle.kts

@@ -1,13 +1,8 @@
-import org.jetbrains.kotlin.gradle.ExperimentalKotlinGradlePluginApi
-
 plugins {
   id("arrow.kotlin")
 }
 
 kotlin {
-  @OptIn(ExperimentalKotlinGradlePluginApi::class)
-  compilerOptions.freeCompilerArgs.add("-Xexpect-actual-classes")
-
   sourceSets {
     commonTest {
       dependencies {

arrow-libs/core/arrow-atomic/src/nonJvmMain/kotlin/arrow/atomic/Atomic.kt

@@ -0,0 +1,20 @@
+@file:OptIn(ExperimentalAtomicApi::class)
+
+package arrow.atomic
+
+import kotlin.concurrent.atomics.ExperimentalAtomicApi
+import kotlin.concurrent.atomics.AtomicReference as KtAtomicReference
+
+public actual class Atomic<V> actual constructor(initialValue: V) {
+  private val inner = KtAtomicReference(initialValue)
+
+  public actual fun get(): V = inner.load()
+  public actual fun set(value: V) { inner.store(value) }
+  public actual fun getAndSet(value: V): V = inner.exchange(value)
+
+  /**
+   * Compare current value with expected and set to new if they're the same. Note, 'compare' is checking
+   * the actual object id, not 'equals'.
+   */
+  public actual fun compareAndSet(expected: V, new: V): Boolean = inner.compareAndSet(expected, new)
+}

arrow-libs/core/arrow-atomic/src/nonJvmMain/kotlin/arrow/atomic/AtomicInt.kt

@@ -0,0 +1,23 @@
+@file:OptIn(ExperimentalAtomicApi::class)
+
+package arrow.atomic
+
+import kotlin.concurrent.atomics.ExperimentalAtomicApi
+import kotlin.concurrent.atomics.decrementAndFetch
+import kotlin.concurrent.atomics.incrementAndFetch
+import kotlin.concurrent.atomics.AtomicInt as KtAtomicInt
+
+public actual class AtomicInt actual constructor(initialValue: Int) {
+  private val inner = KtAtomicInt(initialValue)
+
+  public actual fun get(): Int = inner.load()
+  public actual fun set(newValue: Int) { inner.store(newValue) }
+  public actual fun getAndSet(value: Int): Int = inner.exchange(value)
+
+  public actual fun incrementAndGet(): Int = inner.incrementAndFetch()
+  public actual fun decrementAndGet(): Int = inner.decrementAndFetch()
+
+  public actual fun addAndGet(delta: Int): Int = inner.addAndFetch(delta)
+
+  public actual fun compareAndSet(expected: Int, new: Int): Boolean = inner.compareAndSet(expected, new)
+}

arrow-libs/core/arrow-atomic/src/nonJvmMain/kotlin/arrow/atomic/AtomicLong.kt

@@ -0,0 +1,23 @@
+@file:OptIn(ExperimentalAtomicApi::class)
+
+package arrow.atomic
+
+import kotlin.concurrent.atomics.AtomicLong as KtAtomicLong
+import kotlin.concurrent.atomics.ExperimentalAtomicApi
+import kotlin.concurrent.atomics.decrementAndFetch
+import kotlin.concurrent.atomics.incrementAndFetch
+
+public actual class AtomicLong actual constructor(initialValue: Long) {
+  private val inner = KtAtomicLong(initialValue)
+
+  public actual fun get(): Long = inner.load()
+  public actual fun set(newValue: Long) { inner.store(newValue) }
+  public actual fun getAndSet(value: Long): Long = inner.exchange(value)
+
+  public actual fun incrementAndGet(): Long = inner.incrementAndFetch()
+  public actual fun decrementAndGet(): Long = inner.decrementAndFetch()
+
+  public actual fun addAndGet(delta: Long): Long = inner.addAndFetch(delta)
+
+  public actual fun compareAndSet(expected: Long, new: Long): Boolean = inner.compareAndSet(expected, new)
+}