refactor - reimplements ObservableCreate using Observation

lib/src/dart_observable/observables/observable_create.dart

@@ -3,6 +3,7 @@ import 'package:meta/meta.dart';
 import 'package:disposal/disposal.dart';
 
 import 'observable.dart';
+import 'observation.dart';
 import '../observers/observer.dart';
 
 @internal
@@ -14,21 +15,45 @@ class ObservableCreate<T> implements Observable<T> {
 
   @override
   Disposable observe(OnData<T> onData) {
-    bool disposed = false;
-
-    final observation = _observe((data) {
-      if (disposed) {
-        return;
-      }
-      onData(data);
-    });
-
-    return Disposable(() {
-      if (disposed) {
-        return;
-      }
-      disposed = true;
-      observation.dispose();
-    });
+    return _Observation<T>(
+      observe: _observe,
+      emit: onData,
+    );
+  }
+}
+
+class _Observation<T> extends Observation<T> implements Observer<T> {
+
+  _Observation({
+    required Observe<T> observe,
+    required OnData<T> emit,
+  }): _observe = observe,
+    super(emit: emit);
+
+  final Observe<T> _observe;
+
+  bool _disposed = false;
+  late final Disposable _sourceObservation;
+
+  @override
+  void init() {
+    _sourceObservation = _observe(onData);
+  }
+
+  @override
+  void onData(T data) {
+    if (_disposed) {
+      return;
+    }
+    emit(data);
+  }
+
+  @override
+  void dispose() {
+    if (_disposed) {
+      return;
+    }
+    _disposed = true;
+    _sourceObservation.dispose();
   }
 }