Composition

Go gives us the ability to embed interfaces into interfaces, interfaces into structs, and structs into other structs.

Embedding structs and Acessing Embedded fields

Employee and Person struct has fields which are common. We can thereby define a new Name struct which holds these fields and embed the Name struct in the Employee and Person structs.

We can also define a FullName method on the Name struct which the Employee and Person struct has access to.

// Name struct : Name struct
type Name struct {
	first string
	last  string
}

// FullName : returns the first and last fields of the Name struct
func (n Name) FullName() string {
	return fmt.Sprintf("%s %s", n.first, n.last)
}

// Employee : Employee struct
type Employee struct {
	Name
}

// Person : Person struct
type Person struct {
	Name
	twitterHandler TwitterHandler
}

// NewPerson : returns the Person object
func NewPerson(firstName, lastName string) Person {
	return Person{
		Name: Name{
			first: firstName,
			last:  lastName,
		},
	}
}

Embedding interfaces

We can embed an interface into a struct type. There is no field on an interface, we're embedding the method sets of the interface on the struct type.

// Identifiable : Identifiable interface
type Identifiable interface {
	ID() string
}

// Person : Person struct
type Person struct {
	Name
	twitterHandler TwitterHandler
	Identifiable
}

We can also embed an interface into a interface

// Identifiable : Identifiable interface
type Identifiable interface {
	ID() string
}

// Citizen : Citizen interface
type Citizen interface {
	Identifiable
	Country() string
}