工厂方法模式是简单工厂的升级。他创建一个用于实例化类的接口，并由工厂的子类决定实例化哪个类。工厂方法模式使得一个类的实例化延迟到子类。
下面仍然以“两个数字的运算”作为例子
operations.go // 运算类
package factory_method
// 运算
type Operation interface {
SetA(float64)
SetB(float64)
GetResult() (float64, error)
}
// 运算基类，实现公共的方法
type OperationBase struct {
a float64
b float64
}
func (oper *OperationBase) SetA(a float64) {
oper.a = a
}
func (oper *OperationBase) SetB(b float64) {
oper.b = b
}
// 加法运算
type AddOperation struct {
*OperationBase
}
func (oper *AddOperation) GetResult() (float64, error) {
return oper.a + oper.b, nil
}
// 减法运算
type SubOperation struct {
*OperationBase
}
func (oper *SubOperation) GetResult() (float64, error) {
return oper.a - oper.b, nil
}
// 乘法元算
type MulOperation struct {
*OperationBase
}
func (oper *MulOperation) GetResult() (float64, error) {
return oper.a * oper.b, nil
}
factory_method.go // 工厂类
package factory_method
// 工厂类
type OperationFactory interface {
CreateOperation() Operation
}
// 加法工厂
type AddFactory struct {
}
func (f *AddFactory) CreateOperation() Operation {
return &AddOperation{
OperationBase: &OperationBase{},
}
}
// 减法工厂
type SubFactory struct {
}
func (f *SubFactory) CreateOperation() Operation {
return &SubOperation{
OperationBase: &OperationBase{},
}
}
// 乘法工厂
type MulFactory struct {
}
func (f *MulFactory) CreateOperation() Operation {
return &MulOperation{
OperationBase: &OperationBase{},
}
}
源码以及测试源码下载地址：https://github.com/h1z3y3/big-talk-go-design-patterns/tree/master/04_factory_method