Why can't I use the as keyword for a struct?

Question

I defined the following struct:

public struct Call
{
    public SourceFile caller;
    public SourceFile callee;

    public Call(SourceFile caller, SourceFi         


        

Answer 1

A struct is a value type, so it cannot be used with the as operator. The as operator must be able to assign a value of null if the cast fails. This is only possible with a reference type or a nullable value type.

There are a couple ways to solve this, but your best bet is to change your Call type from a struct to a class. This will essentially change your type from a value type to a reference type, which allows the as operator to assign a value of null if the cast fails.

For more information on value types vs. reference types, this is a decent article. Also, have a look on MSDN:

• value types
• reference types
• as-operator
• nullable types.