Passing Objects by Value

Question

I am trying to work through an example in a book and have run across something that just doesn't make sense. In the method listed below, I am passing in a object of type Fraction. public override bool Equals(object o) { if (!(o is Fraction)) { return false; } // Console.WriteLine(o.GetType()); return this ==(Fraction) o; } What I don't understand is why the cast in the last line. If I take the cast out I get the following error: 'Possible unintended reference comparison; to get a value comparison, cast the right hand side to type 'ConsoleApplication18.Fraction' If I uncomment the Console.Writeline it tells me 'o' is of type Fraction. In addition, the error message makes it sound like if I cast to Fraction then the value comparison will be ok. But Fraction is an object and therefore a reference type not a value type. Can someone explain this to me.

Administrator · Answer

Thanks. I think it makes about as much sense as it can. More importantly I understand enough to move on.

Administrator · Answer

Hi I don't think it's a 'reference type' - its a reference TO a Fraction. In the method signiature you have said its an Object....which means it will stay as an Object until you explicitly cast it to something else. GetType will tell you the underlyng object type. That's pretty useful when you want to pass multiple related object types into a single method...let the method figure out the specific class type. Without the cast you are comparing two different class types. Hope this makes sense.