When should you use NEW?

I don't understand when, in Unity, it is appropriate to use "new" For example, if I fire a rocket, I instantiate a prefab of a rocket. If I want to have a "frog" I would drop a "frog.cs" script onto a gameobject.

When is it appropriate in Unity to use the new keyword?

(from - http://unity3d.com/learn/tutorials/modules/beginner/scripting/data-types )

Code (CSharp):

1. public class DatatypeScript : MonoBehaviour
2. {
3.     void Start ()
4.     {
5.         //Value type variable
6.         Vector3 pos = transform.position;
7.         pos = new Vector3(0, 2, 0);
8.    
9.         //Reference type variable
10.         Transform tran = transform;
11.         tran.position = new Vector3(0, 2, 0);
12.     }
13. }

(from - https://unity3d.com/learn/tutorials/modules/beginner/scripting/classes )

Code (CSharp):

1.   public Stuff myStuff = new Stuff(50, 5, 5);
2.    
3.     public Stuff myOtherStuff = new Stuff(50, 1.5f);
4.    

 

When you are creating a new object for the most part. Ideally, for beginners, anytime in C# that you encounter a situation to use Vector3, you have to use the new keyword.

Setting position, rotation, and scale require a "new" vector3.

If you want to create an object , you have to do so using a constructor through the "new" keyword

 

In Unity, for the most part you use "new" when you want to instantiate an object or create a struct that doesn't derive from MonoBehaviour.

 

Adding to what Fajlworks said above, the way to create a new Monobehavior-derived class is to use the .AddComponent<T>() method on a GameObject, which does the necessary behind-the-scenes plumbing to integrate the new Monobehavior with the given game object.