[Noob] Collision Trigger in Player or Coin ?

Hi,

I'm starting with unity and i have some questions.

Is it better to check for collision in Player or in prefabs Coin ? (The player can catch coins.)


Player :

Code (CSharp):

1.     void OnTriggerEnter2D(Collider2D obj)
2.     {
3.         switch (obj.tag) {
4.         case "Coin":
5.             Destroy(obj.gameObject);
6.             Global.score++;
7.             break;
8.         }
9.     }

Coin :

Code (CSharp):

1. void OnTriggerEnter2D()
2.     {
3.             Destroy(gameObject);
4.             Global.score++;
5.     }

And in the seconde case it increases score by 2. I guess because it takes both player and Coin but is there a mean to trigger this script only once when collision ?
(Edit : Ok for this one, I thaught that unthicking a script would desactivate it )

Is it bad for performance to let empty functions like : update{ } ?

Is there a mean to show errors in MonoDevelop ?

Why when a block is quite fast, it can pass through other rigid blocks ?


Thanks !
Have a nice day !

 

Because physics updates happen in steps rather than continuously like in real life.

 

Thanks for your replies, any idea for the other questions ?

The first question
and
"Is it bad for performance to let empty functions like : update{ } ?"