C# 3.0 Cookbook, 3rd Edition

3.9. Determining When to Use the cast Operator, the as Operator, or the is Operator

Problem

You need to determine which operator is best in your situation—the cast (type) operator, the as operator, or the is operator.

Solution

Use the information provided in the Discussion section to determine which operator is best to use.

Discussion

Use the cast operator when:

• You are converting a reference type to a reference type.

• You are converting a value type to a value type.

• You are performing a boxing or unboxing conversion.

• You are invoking a user-defined conversion. The is and as operators cannot handle this type of cast.

Use the as operator when:

• It is not acceptable for the InvalidCastException to be thrown. The as operator will instead return a null if the cast cannot be performed.

• You are converting a reference type to a reference type.

• You are not casting a value type to a value type. The cast operator must be used in this case.

• You are performing a boxing conversion.

• You are not performing an unboxing conversion. The cast operator must be used in this case unless the unboxing is to a nullable type.

• You are not invoking a user-defined conversion. The cast operator must be used in this case.

• You are performing a cast to a type parameter T that can be only a reference type. This is because a null may be returned after evaluating this expression.

Use the is operator when:

• You need a fast method of determining whether using the as operator will return null before it is attempted.

• You do not need to actually ...