Interface Pollution Detection
Interface pollution occurs when interfaces are created before they're needed. Define interfaces at consumption point, not production.
Pollution Patterns
WRONG - Producer defines interface prematurely
go
// In package "storage"
type UserRepository interface {
GetUser(id int) (*User, error)
SaveUser(u *User) error
}
type PostgresRepo struct{}
func (p *PostgresRepo) GetUser(id int) (*User, error) { ... }
func (p *PostgresRepo) SaveUser(u *User) error { ... }
CORRECT - Consumer defines minimal interface
go
// In package "handler"
type UserGetter interface {
GetUser(id int) (*User, error)
}
func HandleRequest(repo UserGetter) http.Handler {
// Only needs GetUser, not entire repository
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
user, _ := repo.GetUser(123)
// ...
})
}
// Concrete type lives in storage package
// Handler depends on small interface, not full implementation
Detection Checklist
You have interface pollution if:
- • Interface defined in same package as implementation
- • Only one implementation exists
- • Interface has >5 methods
- • Name ends in "Interface" or "Impl"
Refactoring Strategy
Before:
go
type DataService interface {
Read() error
Write() error
Validate() error
Transform() error
}
After:
go
// Split by actual usage
type Reader interface { Read() error }
type Writer interface { Write() error }
// Compose where needed
type ReadWriter interface {
Reader
Writer
}