♻️ (SINGLETON) Add support to singletons

container.go

@@ -9,6 +9,7 @@ import (
 // Container holds the registered factories for dependency resolution.
 type Container struct {
 	providers map[reflect.Type]reflect.Value
+	instances map[reflect.Type]reflect.Value
 }
 
 // New initializes and returns a new instance of the Container.
@@ -18,9 +19,11 @@ type Container struct {
 //	c := zeus.New()
 func New() *Container {
 	providers := make(map[reflect.Type]reflect.Value, 0)
+	instances := make(map[reflect.Type]reflect.Value, 0)
 
 	container := new(Container)
 	container.providers = providers
+	container.instances = instances
 
 	return container
 }
@@ -67,6 +70,10 @@ func (c *Container) resolve(t reflect.Type, stack []reflect.Type) (reflect.Value
 		return reflect.Value{}, CyclicDependencyError{TypeName: t.Name()}
 	}
 
+	if instance, exists := c.instances[t]; exists {
+		return instance, nil
+	}
+
 	provider, ok := c.providers[t]
 
 	if !ok {
@@ -93,6 +100,8 @@ func (c *Container) resolve(t reflect.Type, stack []reflect.Type) (reflect.Value
 		return reflect.Value{}, results[1].Interface().(error)
 	}
 
+	c.instances[t] = results[0]
+
 	return results[0], nil
 }
 

container_test.go

@@ -106,6 +106,40 @@ func TestContainer(t *testing.T) {
 
 			assert.ErrorContains(t, err, "some error")
 		})
+
+		t.Run("Shared Instance Between Dependencies", func(t *testing.T) {
+			c := New()
+
+			type ServiceC struct{}
+			type ServiceB struct {
+				C *ServiceC
+			}
+			type ServiceA struct {
+				C *ServiceC
+			}
+
+			c.Provide(func() *ServiceC {
+				return &ServiceC{}
+			})
+			c.Provide(func(c *ServiceC) *ServiceA {
+				return &ServiceA{C: c}
+			})
+			c.Provide(func(c *ServiceC) *ServiceB {
+				return &ServiceB{C: c}
+			})
+
+			aVal, _ := c.resolve(reflect.TypeOf(&ServiceA{}), nil)
+			bVal, _ := c.resolve(reflect.TypeOf(&ServiceB{}), nil)
+
+			a, ok := aVal.Interface().(*ServiceA)
+			assert.Equal(t, ok, true)
+
+			b, ok := bVal.Interface().(*ServiceB)
+			assert.Equal(t, ok, true)
+
+			assert.Equal(t, a.C, b.C)
+		})
+
 	})
 
 	t.Run("Run", func(t *testing.T) {