观察者模式

package observer

import (
    "container/list"
    "fmt"
)

type Subject interface {
    RegisterObserver(o Observer)
    RemoveObserver(o Observer)
    NotifyObserver()
}

type Observer interface {
    Update()
}

type DisplayElement interface {
    Display()
}

/////////////////////////////////////

type WeatherData struct {
    o *list.List
    t int // temperature
    h int // humidity
    p int // pressure
}

func NewWeatherData() *WeatherData {
    r := new(WeatherData)
    r.o = new(list.List)
    return r
}

func (o *WeatherData) RegisterObserver(ob Observer) {
    o.o.PushBack(ob)
}

func (o *WeatherData) RemoveObserver(ob Observer) {
    for e := o.o.Front(); e != nil; e = e.Next() {
        if e.Value == ob {
            o.o.Remove(e)
            return
        }
    }
}

func (o *WeatherData) NotifyObserver() {
    for e := o.o.Front(); e != nil; e = e.Next() {
        e.Value.(Observer).Update()
    }
}

//////////////////////////////////////

type CurrentConditionsDisplay struct {
}

func (o *CurrentConditionsDisplay) Update() {
    o.Display()
}

func (o *CurrentConditionsDisplay) Display() {
    fmt.Println("CurrentConditionsDisplay update!")
}

type StatisticsDisplay struct {
}

func (o *StatisticsDisplay) Update() {
    o.Display()
}

func (o *StatisticsDisplay) Display() {
    fmt.Println("StatisticsDisplay update!")
}

type ForecastDisplay struct {
}

func (o *ForecastDisplay) Update() {
    o.Display()
}

func (o *ForecastDisplay) Display() {
    fmt.Println("ForecastDisplay update!")
}

type ThirdPartyDisplay struct {
}

func (o *ThirdPartyDisplay) Update() {
    o.Display()
}

func (o *ThirdPartyDisplay) Display() {
    fmt.Println("ThirdPartyDisplay update!")
}