vue计算属性computed--getter和setter用法

      computed: {
        propsName: {
          a:['aavsx'],
          get(){
            return this.a;
          },
          set(val){
            this.a = val
          }
        },
      }

<template>
    <div>
    {{propsName = 'add'}} //结果是add
    {{propsName}}//结果是 a ，以为set方法没有改变this.a这个依赖
    </div>
</template>

<script>
export default {
  data(){
    return {
      a:'a',
      b:'b'
    }
  },
  computed: {
    propsName: {
      get(){
        return this.a
      },
      set(val){
       this.b = val
      }
    },
  }
}
</script>

computed: {
  propName(){
    // getter
    //必须要有返回值
  }
}

   const { effect, reactive,computed } = VueReactivity

        const state = reactive({
            firstName:'s',
            lastName:'x'
        })
        let fullName = computed(()=>{
            console.log('runner')
            return state.firstName + state.lastName
        })
        console.log(fullName.value)
        console.log(fullName.value)
        console.log(fullName.value)

 const { effect, reactive,computed } = VueReactivity

        const state = reactive({
            firstName:'s',
            lastName:'x'
        })
       
        let fullName = computed({
            get(){
                return state.firstName + state.lastName
            },
            set(value){
                state.lastName = value
            }
        })
        fullName.value = 100
        effect(()=>{
            app.innerHTML = fullName.value
        })
        setTimeout(()=>{
            state.firstName = 'x'
        },1000)

import { isFunction } from "@vue/shared"
import { activeEffect, trackEffects, triggerEffects,ReactiveEffect } from "./effect";

export function computed(getterOrOptions){
    let getter = null;
    let setter = null;
    let fn = ()=>{
        throw new Error("this function is onlyRead");
        
    }
    let isGetter = isFunction(getterOrOptions)
    if(isGetter){
        getter = getterOrOptions
        setter = fn
    }
    else {
        getter = getterOrOptions.get
        setter = getterOrOptions.set || fn
    }

    return new computedRefImpl(getter,setter)
}

class computedRefImpl{
    private _value = null
    private _dirty = true
    public effect = null
    public deps = null
    constructor(getter,public setter){
        this.effect = new ReactiveEffect(getter,()=>{
            if(!this._dirty){
                this._dirty = true
                triggerEffects(this.deps)
            }
        })
    }
    get value(){
        debugger
        if(activeEffect){
            // 存在effect，则进行依赖收集
            trackEffects(this.deps ||  (this.deps = new Set()) )
        }
        if(this._dirty){
            this._dirty = false
            this._value = this.effect.run()
        }
        return this._value
    }
    set value(newValue){
        this.setter(newValue)
    }
}