Support for DI default values

Author: wkornewald

README.md

@@ -1,6 +1,6 @@
 # ReactiveState
 
-[![Maven Central](https://img.shields.io/maven-central/v/com.ensody.reactivestate/reactivestate-core)](https://central.sonatype.com/artifact/com.ensody.reactivestate/reactivestate-core-android)
+[![Maven Central](https://img.shields.io/maven-central/v/com.ensody.reactivestate/reactivestate-core?color=%2345cf00)](https://central.sonatype.com/artifact/com.ensody.reactivestate/reactivestate-core)
 
 Kotlin Multiplatform ViewModels and reactive state management based on `StateFlow`.
 

reactivestate-core/src/commonMain/kotlin/com/ensody/reactivestate/DI.kt

@@ -118,10 +118,17 @@ public class DIImpl {
         }
 
     // We hide this function as an extension, so nobody can mistakenly get() arbitrary T values not belonging to the DI
-    public inline fun <reified T : Any> DIResolver.get(): LazyProperty<T> =
-        InternalDI.run { get(this@get, T::class) }
-
-    public fun <T : Any> InternalDI.get(resolver: DIResolver, klass: KClass<T>): LazyProperty<T> {
+    public inline fun <reified T : Any> DIResolver.get(noinline default: (() -> T)? = null): LazyProperty<T> =
+        InternalDI.run { get(this@get, T::class, default) }
+
+    public fun <T : Any> InternalDI.get(
+        resolver: DIResolver,
+        klass: KClass<T>,
+        default: (() -> T)? = null,
+    ): LazyProperty<T> {
+        if (default != null && klass !in deps) {
+            register(klass) { default() }
+        }
         val state = deps.getValue(klass)
         resolver.run { owner }?.also {
             // A DI module/node must not resolve any deps eagerly, so we can support circular dependencies.

reactivestate-core/src/commonTest/kotlin/com/ensody/reactivestate/DITest.kt

@@ -13,17 +13,21 @@ internal class DITest {
     val testDI = DIImpl()
 
     init {
-        testDI.register { FooDeps(get(someConfigFlag), barDeps) }
+        testDI.register { FooDeps(get(someConfigFlag), barDeps, defaultDeps) }
         testDI.register { BarDeps(fooDeps) }
     }
 
+    private val defaultFlow = testDI.derived { get(defaultDeps) }
+    private val default = defaultFlow.value
     private val fooFlow = testDI.derived { get(fooDeps) }
     private val foo = fooFlow.value
     private val barFlow = testDI.derived { get(barDeps) }
     private val bar = barFlow.value
 
     @Test
     fun stability() {
+        assertSame(default, testDI.derived { get(defaultDeps) }.value)
+        assertSame(default, foo.defaultDeps)
         assertSame(foo, testDI.derived { get(fooDeps) }.value)
         assertSame(bar, testDI.derived { get(barDeps) }.value)
     }
@@ -37,16 +41,17 @@ internal class DITest {
         testDI.register {
             // This causes a too early access
             get(barDeps)
-            FooDeps(get(someConfigFlag), barDeps)
+            FooDeps(get(someConfigFlag), barDeps, defaultDeps)
         }
         assertFailsWith<IllegalStateException> { barFlow.value.configFlag }
     }
 
     @Test
     fun updateDIGraphOnRegister() {
         // Replacing FooDeps invalidates the whole subgraph depending on FooDeps. So, BarDeps gets re-created.
-        testDI.register { FooDeps(get(someConfigFlag), barDeps) }
+        testDI.register { FooDeps(get(someConfigFlag), barDeps, defaultDeps) }
         assertNotSame(foo, testDI.derived { get(fooDeps) }.value)
+        assertSame(default, testDI.derived { get(fooDeps) }.value.defaultDeps)
         val newBar = testDI.derived { get(barDeps) }.value
         assertNotSame(bar, newBar)
         assertTrue(foo.circularConfigFlag)
@@ -72,6 +77,16 @@ internal class DITest {
     }
 }
 
+// -------------
+// module DefaultDeps
+// -------------
+
+// Convenience accessor for FooDeps
+private val DIResolver.defaultDeps: LazyProperty<DefaultDeps>
+    get() = DI.run { get { DefaultDeps() } }
+
+private class DefaultDeps(val value: Boolean = true)
+
 // -------------
 // module foo
 // -------------
@@ -83,9 +98,11 @@ private val DIResolver.fooDeps: LazyProperty<FooDeps> get() = DI.run { get() }
 private class FooDeps(
     val configFlag: Boolean,
     lazyBarDeps: LazyProperty<BarDeps>,
+    lazyDefaultDeps: LazyProperty<DefaultDeps>,
 ) {
     // All deps have to be resolved lazily
     val barDeps by lazyBarDeps
+    val defaultDeps by lazyDefaultDeps
 
     // All deps have to be resolved lazily
     val circularConfigFlag by lazy { barDeps.configFlag }