Question

Possible Duplicates:
Casting: (NewType) vs. Object as NewType
Why is the C# “as” operator so popular?

Hey,

I know this may be a silly question but this doubt came to me today.

What is the difference between doing

String text = (String) variable;

and

String text = variable as String;

?

Answer 1

A cast can do three things:

• Perform a user-defined conversion
• Perform an unboxing conversion
• Perform a reference conversion

An as operation is almost always a reference conversion, the only exception being unboxing to a nullable type:

object x = "hello";
int? y = x as int?; // y is null afterwards

Then there’s the behaviour with conversions which fail at execution time. So the differences are:

• Casts performing reference conversions or unboxing will throw InvalidCastException on failure; as will result in the null value of the target type instead
• Casts can perform user-defined conversions; as can’t
• Casts can unbox to non-nullable value types; as can only be used for unboxing if the target type is a nullable value type