Fix interface constructor bug

Author: DerekGooding

SimpleInjection/Injection/Host.cs

@@ -178,7 +178,27 @@ private void CreateSingletonFactory(ServiceDescriptor descriptor)
         {
             if (!_singletonInstances.TryGetValue(serviceType, out var instance))
             {
-                instance = CreateInstance(serviceType, scope);
+                var typeToCreate = serviceType;
+                if (serviceType.IsInterface)
+                {
+                    // Find all concrete implementations for this interface
+                    var implementations = _serviceDescriptors
+                        .Where(sd => serviceType.IsAssignableFrom(sd.ServiceType) && !sd.ServiceType.IsInterface && !sd.ServiceType.IsAbstract)
+                        .ToList();
+                    if (implementations.Count == 1)
+                    {
+                        typeToCreate = implementations[0].ServiceType;
+                    }
+                    else if (implementations.Count > 1)
+                    {
+                        throw new InvalidOperationException($"Multiple implementations found for interface {serviceType.Name}. Please register only one or use a more specific type.");
+                    }
+                    else
+                    {
+                        throw new InvalidOperationException($"No implementation found for interface {serviceType.Name}.");
+                    }
+                }
+                instance = CreateInstance(typeToCreate, scope);
                 _singletonInstances[serviceType] = instance;
             }
             return instance;

SimpleInjection/SimpleInjection.csproj

@@ -8,7 +8,7 @@
 
 	<GeneratePackageOnBuild>true</GeneratePackageOnBuild>
 	<PackageId>SimpleInjection</PackageId>
-	<Version>0.9.6.2</Version>
+	<Version>0.9.6.3</Version>
 	<Authors>Derek Gooding</Authors>
 	<Company>Derek Gooding</Company>
 	<Description>