Possible Duplicate:
Casting: (NewType) vs. Object as NewType
Casting vs using the 'as' keyword in the CLR
What is the difference between these 2 types of conversion(as i've seen, they don't work both all the time) :
ClassA a = (ClassA)someClassObject;
and
ClassA a = someClassObject as ClassA
Per http://msdn.microsoft.com/en-us/library/cscsdfbt%28v=vs.71%29.aspx (emphasis mine):
The as operator is like a cast except that it yields null on conversion failure instead of raising an exception. More formally, an expression of the form:
expression as typeis equivalent to:
expression is type ? (type)expression : (type)nullexcept that expression is evaluated only once.
In the first case an InvalidCastException will be thrown at runtime if the cast doesn't succeed. In the second case you will get null in the result variable.
The first is casting - if someClassObject cannot be cast, an InvalidCastException will be thrown.
The second will not throw an exception, but a will be null if the cast does not succeed.
