What is the different between this two script.

Hello there, I would like to know the different between this two script.

The first one (First time seeing it. Is it the same as the second one, or there's a different)

Code (csharp):

1.  
2. Transform gObject;
3.  
4. gObject= (Transform) Instantiate (floor, new Vector3 (iFloor, 0, iFloor2), Quaternion.identity);
5.  

The second one: (i've seen this alot and i'm using this as well)

Code (csharp):

1.  
2. Transform gObject;
3.  
4. gObject= Instantiate (floor, new Vector3 (iFloor, 0, iFloor2), Quaternion.identity) as Transform;
5.  

 

nothing.

just a different style of casting


note: not sure if underlying they are slightly different, but I expect they are not.

in c# there is also an 'is' keyword, so it pairs up nicely with the second method

Code (csharp):

1.  
2.  
3. if(object is GameObject)
4. {
5.   (object as GameObject).stuff();
6. }
7.  
8.  

 

Thanks JamesLeeNZ..now I understand.

 

The second is recommend.
for example，TypeA instanceA = (TypeA)InstanceB,if instanceB is not TypeA(can't be cast to TypeA),there will be an exception.the second ,"TypeA instanceA = InstanceB as TypeA",instanceA will be null.
So,we can write code like this

Code (csharp):

1.  
2. TypeA instanceA = instanceB as TypeA;
3. if(instanceA != null)
4. {
5. do something;
6. }
7.  

 

What? Exceptions are good, they don't allow you to make incorrect casts. If you already know instanceB is not null, then you save an extra if check if you know what type it is. If you're in a position of not knowing if the object you are casting too is not the correct type, that's just sloppy programming.

 

Exceptions are good just for some time.

consider there's situation like this:
TypeB TypeC inherate TypeA,you need to use TypeB or TypeC but there's instance of TypeA,we can write code like this:

Code (csharp):

1.  
2. TypeB instanceB = instanceA as TypeB;
3. if(instanceB != null)
4. {}
5. TypeC instanceC = instanceA as TypeC;
6. if(instanceC != null)
7. {}
8.  

Exceptions are good but not for every time.sometimes we just don't need exceptions.If we must be certain the type casting is valid, we can add else or use "is".exceptions are not needed.

Code (csharp):

1.  
2. TypeB instanceB = instanceA as TypeB;
3. if(instanceB != null)
4. {}
5. else
6. {
7. error report
8. }
9.  

Bill Wagner wrote a book "Effective C#",Item 3: Item Prefer the is or as Operators to Casts