老师为什么您视频里面的这句话

using UnityEngine;
public class Shoot : MonoBehaviour {
    public GameObject bullet;
    public float speed = 5;
	// Use this for initialization
	void Start () {
       
    }	
	// Update is called once per frame
	void Update () {
        if (Input.GetMouseButtonDown(0))
        {
            GameObject b =(GameObject)Instantiate(bullet, transform.position, transform.rotation);
            Rigidbody rgd = b.GetComponent<Rigidbody>();
            rgd.velocity = transform.forward * speed;
        }
	}
}

第十三行的GameObject b =(GameObject)Instantiate(bullet, transform.position, transform.rotation);没有加括号VS不会报错 而我编辑的时候输入GameObject b =GameObject.Instantiate(bullet, transform.position, transform.rotation);就会报错  去群里面问了几为大佬才知道要强制转换，但为什么您的视频里面不需要转换呢。