collision detection unity 3d code example

Example 1: unity how to tell when a gameobject is colliding

void OnCollisionEnter(Collision collision){
        //Check for a match with the specified name on any GameObject that collides with your GameObject
        if (collision.gameObject.name == "MyGameObjectName")
        {
            //If the GameObject's name matches the one you suggest, output this message in the console
            Debug.Log("Do something here");
        }

        //Check for a match with the specific tag on any GameObject that collides with your GameObject
        if (collision.gameObject.tag == "MyGameObjectTag")
        {
            //If the GameObject has the same tag as specified, output this message in the console
            Debug.Log("Do something else here");
        }
    }

Example 2: unity how to make two objects not collide

void OnCollisionEnter(Collision collision)
  {
      if (collision.gameObject.tag == "theobjectToIgnore")
      {
          Physics.IgnoreCollision(theobjectToIgnore.collider, collider);
      }

Example 3: collision detector unity c# 2d

void OnCollisionEnter2D(Collision2D coll){)