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

It's a limitation of C#. If the type were a reference type, then if the cast failed it would simply return 'null', but since it's a value type, it doesn't know what to return when the cast fails.

You must replace your use of as with two: 'is' and 'as'

if (line.Tag is Call) {
  call = (Call)line.Tag;
} else {
  // Do whatever you would do if as returned null.
}