C# tip - 6/22/2010

Advantages and disadvantages of is, as, and cast operations.

is - used to checked whether an object is a specific type

Object t;

if(t is SomeType){...}

• Advantages
• checks an object without an overhead of a try/catch block
• Disadvantages
• doesn't actually cast anything

as - used to cast reference objects from one type to another

Object t;

t as SomeType

if(t != null) {...}

• Advantages
• casts an object without an overhead of a try/catch block (returns null if cast fails)
• Disadvantages
• cannot be used on value types

cast - used to cast values from one type to another

• Advantages
• can be used to cast any types of values, whether reference or value.  Used in foreach loops for that reason (since collections could have either type)
• ability to fail out of the class when casting an unexpected object is attempted 
• Disadvantages
• try/catch overhead
• may force to insert business logic into the catch block