<template>
    <div>{{count}}</div>
</template>    
<script>
　　import {ref} from 'vue'

    export default {
        setup(){
            const count = ref(10)
            console.log(count.value)     // 10  
        }
    }
</script>        

<script>
　　import {ref, watch} from 'vue'

    export default {
        setup(){
            const arr = [1,2,3]
            setTimeout(() => {
               arr.value[0] = 0
            }, 1500)
            watch(arr, (nelVal) => {   // 监听不到arr的变化
       
            })
        }
    }
</script>        

      

（1）craeteRef 创建ref对象（将基本数据类型转为复杂数据类型）
 function createRef(rawValue, shallow = false) {
    if (isRef(rawValue)) {
        return rawValue;
    }
    return new RefImpl(rawValue, shallow);
 }
（2）RefImpl 类(如果传递 shallow = true 则只是代理最外层)
  class RefImpl {
    constructor(value, _shallow = false) {
        this._shallow = _shallow;
        this.__v_isRef = true;
        this._rawValue = _shallow ? value : toRaw(value);
        this._value = _shallow ? value : convert(value); // const convert = (val) => isObject(val) ? reactive(val) : val;
    }
    get value() {    // value 属性访问器
        track(toRaw(this), "get" /* GET */, 'value');
        return this._value;
    }
    set value(newVal) {  // value 属性设置器
        newVal = this._shallow ? newVal : toRaw(newVal);
        if (hasChanged(newVal, this._rawValue)) {    // 判断新老值是否有变化,改变就更新值,trigger 触发依赖执行
            this._rawValue = newVal;
            this._value = this._shallow ? newVal : convert(newVal);
            trigger(toRaw(this), "set" /* SET */, 'value', newVal);
        }
    }
}