Add initializedOnceBy() to create singleton instances via injection initializer

CHANGES.md

@@ -2,6 +2,7 @@ Poodinis Changelog
 ==================
 **Version 8.1.0-beta.3**
 * CHANGE injection initializers to be defined as a registration scope instead of via Container.register(). See initializedBy().
+* ADD initializedOnceBy() to create singleton instances via injection initializer.
 
 **Version 8.1.0-beta.2**
 * FIX inheritance type template in custom instance creator (PR #29)

source/poodinis/registration.d

@@ -106,7 +106,7 @@ public Registration existingInstance(Registration registration, Object instance)
 }
 
 /**
- * Scopes registrations to create instances using the given initializer delegate.
+ * Scopes registrations to create new instances using the given initializer delegate.
  */
 public Registration initializedBy(T : Object)(Registration registration, T delegate() initializer) {
     registration.instanceFactory.factoryParameters = InstanceFactoryParameters(registration.instanceType, CreatesSingleton.no, null, {
@@ -116,6 +116,17 @@ public Registration initializedBy(T : Object)(Registration registration, T deleg
     return registration;
 }
 
+/**
+ * Scopes registrations to create a new instance using the given initializer delegate. On subsequent resolves the same instance is returned.
+ */
+public Registration initializedOnceBy(T : Object)(Registration registration, T delegate() initializer) {
+    registration.instanceFactory.factoryParameters = InstanceFactoryParameters(registration.instanceType, CreatesSingleton.yes, null, {
+         return cast(Object) initializer();
+    });
+    
+    return registration;
+}
+
 public string toConcreteTypeListString(Registration[] registrations) {
     auto concreteTypeListString = "";
     foreach (registration ; registrations) {

test/poodinis/containertest.d

@@ -80,7 +80,7 @@ version(unittest) {
         assert(expectedInstance is actualInstance, "Resolved instance from existing instance scope is not the same as the registered instance");
     }
 
-    // Test creating instance via customer initializer on resolve
+    // Test creating instance via custom initializer on resolve
     unittest {
         auto container = new shared DependencyContainer();
         auto expectedInstance = new TestClass();
@@ -91,6 +91,28 @@ version(unittest) {
         assert(expectedInstance is actualInstance, "Resolved instance does not come from the custom initializer");
     }
 
+    // Test creating instance via initializedBy creates new instance every time
+    unittest {
+        auto container = new shared DependencyContainer();
+        container.register!TestClass.initializedBy({
+            return new TestClass();
+        });
+        auto firstInstance = container.resolve!TestClass;
+        auto secondInstance = container.resolve!TestClass;
+        assert(firstInstance !is secondInstance, "Resolved instance are not different instances");
+    }
+
+    // Test creating instance via initializedOnceBy creates a singleton instance
+    unittest {
+        auto container = new shared DependencyContainer();
+        container.register!TestClass.initializedOnceBy({
+            return new TestClass();
+        });
+        auto firstInstance = container.resolve!TestClass;
+        auto secondInstance = container.resolve!TestClass;
+        assert(firstInstance is secondInstance, "Resolved instance are different instances");
+    }
+
     // Test autowire resolved instances
     unittest {
         auto container = new shared DependencyContainer();