Casting Syntax Vs AS Operator – Which Approach Is Better And Why ?

The two most popular approaches to casting – converting data types and objects  – in C#  are

1. Using the cast syntax i.e. (TypeToBeCastTo) (type/object) and
2. Using the AS operator i.e. (type/object) AS TypeToBeCastTo

It is speculated that most developers use the first approach, but have you ever wondered which approach is the better one, is more performance efficient, and why ?

According to Jon Skeet (on MSDN), the fundamental difference in the two approaches is as follows.

1. The AS operator returns a null when the variable you are trying to convert is not of the requested type or in it’s inheritance chain. The cast syntax, on the other hand, throws an exception.
2. AS operator can only be used on reference type variables, whereas the cast syntax can be applied to reference and value types.
3. The AS operator also will not be able to perform conversions on user-defined types, whereas the casting syntax will be able to accomplish this.

Performance: According to Jon, the AS operator syntax is known to be slightly faster than the casting syntax in v1.0 and v1.1.

Moreover, to me, it makes sense to use the AS operator where possible also because it does not throw an exception, which are in general very expensive in terms of performance. Lastly, I think the AS syntax also looks “more elegant”.

Further Reading

• Jon Skeet’s C# Frequently Asked Questions
• Ian Griffiths’ essay on C#’s approach to Casting. (1500+ words including code).