Update error messages.

module/context.go

@@ -5,6 +5,8 @@ import (
 	"fmt"
 )
 
+var ErrNoPrivoder = fmt.Errorf("can't find module")
+
 type createPanic struct {
 	key moduleKey
 	err error
@@ -28,7 +30,7 @@ func (c *moduleContext) Value(key any) any {
 
 	provider, ok := c.providers[moduleKey]
 	if !ok {
-		panic(createPanic{key: moduleKey, err: fmt.Errorf("can't find module provideing %q", moduleKey)})
+		panic(createPanic{key: moduleKey, err: ErrNoPrivoder})
 	}
 
 	instance, err := provider.value(c)

module/example_test.go

@@ -135,7 +135,7 @@ func ExampleModule_createWithError() {
 	}
 
 	// Output:
-	// inject error: module *module_test.Cache creates an instance error: new cache error
+	// inject error: creating with module *module_test.Cache: new cache error
 }
 
 func ExampleModule_createWithPanic() {
@@ -187,7 +187,7 @@ func ExampleModule_notExistingProvider() {
 	}
 
 	// Output:
-	// inject error: module module_test.DB creates an instance error: can't find module provideing "module_test.DB"
+	// inject error: creating with module module_test.DB: can't find module
 }
 
 type FileSystem interface {

module/module.go

@@ -44,12 +44,7 @@ func (m Module[T]) Value(ctx context.Context) T {
 		return null
 	}
 
-	ret, ok := v.(T)
-	if !ok {
-		return null
-	}
-
-	return ret
+	return v.(T)
 }
 
 func (m Module[T]) key() moduleKey {

module/repo.go

@@ -44,17 +44,7 @@ func (r *Repo) AddModule(provider Provider) {
 // It returns a new context with all injections. If any module creates an instance with an error, `InjectTo` returns that error with the module name.
 func (r *Repo) InjectTo(ctx context.Context) (ret context.Context, err error) {
 	defer func() {
-		rErr := recover()
-		if rErr == nil {
-			return
-		}
-
-		createErr, ok := rErr.(createPanic)
-		if !ok {
-			panic(rErr)
-		}
-
-		err = fmt.Errorf("module %s creates an instance error: %w", createErr.key, createErr.err)
+		err = r.catchError(recover())
 	}()
 
 	providers := make(map[moduleKey]Provider)
@@ -74,3 +64,16 @@ func (r *Repo) InjectTo(ctx context.Context) (ret context.Context, err error) {
 
 	return
 }
+
+func (r *Repo) catchError(err any) error {
+	if err == nil {
+		return nil
+	}
+
+	createErr, ok := err.(createPanic)
+	if !ok {
+		panic(err)
+	}
+
+	return fmt.Errorf("creating with module %s: %w", createErr.key, createErr.err)
+}