Recipe 3.14 Determining Whether to Use theCast Operator, the as Operator, or theis 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

The cast operator should be used when:

• It is acceptable for the InvalidCastException to be thrown. To prevent this exception from being thrown, consider using either the as or is operators.

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

• You are casting 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.

The as operator should be used 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 casting 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.

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

The is operator should be used when:

• You need a fast method of determining whether a cast can be performed before the actual cast is attempted.

• You do not need to actually cast a variable from one data type to another; you just need to determine if the variable can be cast to a specific type.

• It is not acceptable for the InvalidCastException to be thrown.

• You are casting 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 not invoking a user defined conversion. Unlike the as operator, a compile-time error is not displayed when using the is operator with a user-defined conversion. This is operator will instead always return a false value, regardless of whether the cast can successfully be performed.

See Also

See Recipe 3.15 and Recipe 3.16; see the "( ) Operator," "as Operator," and "is Operator" topics in the MSDN documentation.