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).

stringBuilder sbr = new StringBuilder();
// loop
// more code
// clear sbr variable
sbr.Length = 0;

Why ?

It is a well know fact in the .Net community that using StringBuilder for string concatenation and manipulation is far more efficient that using the string class. The problem arises when you need to clear the StringBuilder variable. For regular string variables, you would simply set the variable equal to “”. However, you cannot do that with the StringBuilder class. Moreover, the StringBuilder does not have a Clear() method as one would expect.

So when using a StringBuilder in a loop, for example, to read from a DataReader and write to a FileStream line by line, you are left with atleast 3 choices.

1. Use the Remove() method, to remove all the characters in the variable.
2. Use new to recreate a new instance of the StringBuilder
3. Use the Clear() method.

Using the Remove() method is not efficient, and could also throw an error if your variable has no characters in it. Using new to recreate the instance is obviously a performance overhead. So Of these 3, I would recommend that the last option.

Using the Clear() method is the safest and most efficient !