mkock

maybeUser, err := repo.LoadUser(42) // Returns interface{}, error
if err != nil { ... }
user, ok := maybeUser.(*User) // Ugly conversion
if !ok { ... }

mkock

var u User
repo := new(UserRepository)
err := repo.Load(42, &u)
if err != nil { ... }

mkock

type UserRepository struct { }

func (u *UserRepository) Load(id uint32, h Hydrater) error {
	row := ... // Run a SELECT by id and retrieve the result in a database.Row.
	return h.Hydrate(row) // h must be a pointer.
}

type User struct {
	ID uint32
	Name string

mkock

type EntityLoader interface {
	Load(id uint32, h Hydrater) error
}

type Hydrater interface {
	Hydrate(database.Row) error
}

mkock

type EntityLoader interface {
	LoadUser(id uint32) (User, error)
	LoadAddress(id uint32) (Address, error)
	LoadPurchaseOrder(id uint32) (PurchaseOrder, error)
}

mkock

type EntityLoader interface {
	Load(id uint32) (interface{}, error)
}

mkock

// University is defined in package schools
type University struct {
	school.School
}

func (u University) Name() string { return "Copenhagen Highschool" }
func (u University) Location() string { return "Copenhagen City Center" }
// func (u University) students() []string { return []string{"George", "Ben", "Louise", "Calvin"} } // Can't redefine.

var _ school.School = University{} // Works!

mkock

cannot use University literal (type University) as type school.School in assignment:
        University does not implement school.School (missing school.students method) 
                have students() []string 
                want school.students() []string

mkock

// School is defined in package school
type School interface {
	Name() string
	Location() string
	students() []string
}

// University is defined in package schools
type University struct {}

mkock

// In zap/zapcore/core.go
type Core interface {
	LevelEnabler
	With([]Field) Core
	Check(Entry, *CheckedEntry) *CheckedEntry
	Write(Entry, []Field) error
	Sync() error
}

// In zap/zapcore/hook.go