Factory Method

Factory method pattern is a creational pattern that uses factory methods to deal with the problem of cerating objects without having to specify the exact class of the object that will be created.

For example, I define an interface Pokemon and I have multiple types of pokemon that can satisfy this interface.

package pokemon

// Pokemon has a list of moves and attack.
type Pokemon interface {
  Moves() []string
  Attack() error
  Level() uint
}

type charmander struct {
  // List of attributes
}

func (c *charmander) Moves() []string {
  return []string{}
}

func (c *charmander) Attack() error {
  return nil
}

func (c *charmander) Level() uint {
  return c.level
}

type squirtle struct {
  // List of attributes
}

func (s *squirtle) Moves() []string {
  return []string{}
}

func (s *squirtle) Attack() error {
  return nil
}

func (s *squirtle) Level() uint {
  return s.level
}

I am going to use a factory method to create Pokemon.

// Pokemons
const (
  Charmander = "CHARMANDER"
  Squirtle   = "SQUIRTLE"
)

// NewPokemon is a factory method.
func NewPokemon(p string) Pokemon {
  switch p {
  case Charmander:
    return &charmander{}
  case Squirtle:
    return &squirtle{}
  default:
    return nil
  }
}