Do not use Go like Java
I have been using Go in the following way (like Java)
type SomeService interface {
DoSomething() string
}
type someServiceImpl struct {
}
func NewSomeService() SomeService {
return &someServiceImpl{}
}
func (*someServiceImpl) DoSomething() string {
return "some-service"
}And from a consumer side, it just refers to the interfaces so that I can swap with a mock struct anytime.
func NewAnotherService(someService SomeService) AnotherService {
return &anotherServiceImpl{someService}
}
// anotherservice_test.go
type someMockService struct{}
func (s *someMockService) DoSomething() string {}
func TestAnotherService(t *testing.T) {
anotherService := &anotherServiceImpl{&someMockService{}}
}But then the problem occurs when I want to add a new method to SomeService.
type SomeService interface {
DoSomething() string
+ DoOtherThing()
}
// ...
+ func (*someServiceImpl) DoOtherThing() {
+ fmt.Println("some-service")
+ }Now I have to refactor everywhere including the test files (e.g., anotherservice_test.go)!
What should I have done
Ok, so what should I have done is
- producers should return a concrete type.
- define interface in the consumer and only define what is used.
For example,
// producer.go
type SomeService struct{}
func NewSomeService() SomeService {
return &SomeService{}
}
func (s SomeService) DoSomething() string {
return "some-service"
}And used in the client/consumer,
// consumer.go
type SomethingDoer interface {
DoSomething() string
}
func NewAnotherService(doer SomethingDoer) AnotherService {
return &AnotherService{doer}
}Now notice that even if I add a new method to SomeService, the consumer is not affected.
// producer.go
type SomeService struct{}
func NewSomeService() SomeService {
return &SomeService{}
}
func (s SomeService) DoSomething() string {
return "some-service"
}
+ // this change won't affect `consumer.go`
+ func (s SomeService) DoAnotherThing() {
+ fmt.Println("some-service")
+ }