Unity using “as” vs “GetComponent<>()”

Question

Hello im new to unity and im learning raycast right now , after checking the documentation here https://docs.unity3d.com/ScriptReference/RaycastHit-triangleIndex.html , i got something that's confusing me , what is the difference between :

 MeshCollider themeshhit = thehit.collider as MeshCollider;
 //
 if (themeshhit == null) {
 Debug.Log (" | themeshhit == null ! | ");
 }   
 //    

and :

 MeshCollider themeshhittwo =  thehit.collider.gameObject.GetComponent<MeshCollider> ();
 //
 if (themeshhittwo == null) {
 Debug.Log (" | themeshhittwo == null ! | ");
 } 
 //  

Both method is working correctly , but i want to know what is the difference between them , and i also want to know which one is better if comparing against speed , compatibility , and ability .

Edit : variable thehit is look similar to this

 RaycastHit thehit;

Answer 1

The correct way to do what you want is the first one :

 MeshCollider theMeshHit = thehit.collider as MeshCollider;

In contrary to simple gameobjects .collider does not call GetComponent when using RaycastHit. The reference of the collider is stored in the object when the Physics.Raycast is called, and .collider is the getter to this collider.

The 2nd piece of code you tried calls a useless .gameobject make it slower.

TL; DR :

• thehit.collider.gameObject.GetComponent<MeshCollider> (); : 1 call to GetComponent + 1 call to .gameobject
• thehit.collider as MeshCollider : 1 cast used