#328 – Copying a struct Will Not Copy Underlying Reference Types

Assigning a struct to a new variable will make a copy of the contents of the struct.  After the assignment, two copies of the struct will exist, which can be changed independently.

If the struct contains any reference-typed fields, only a reference to an object is copied.  Both copies of the struct will then refer to the same object.

Assume that we define the following struct:

        public struct MovieInfo
            public string Title;
            public int Year;
            public Person Director;

If we make a copy of the MovieInfo struct through an assignment, the Director field in the two copies will point to the same Person object.

            MovieInfo goneWithWind;
            goneWithWind.Title = "Gone With the Wind";
            goneWithWind.Year = 1939;
            goneWithWind.Director = new Person("Victor", "Fleming");

            // Actually makes a copy of entire struct
            MovieInfo goodClarkGableFlick = goneWithWind;

            // Change director's name
            goneWithWind.Director.FirstName = "Victoria";

            Console.WriteLine(goneWithWind.Director);            // Victoria Fleming
            Console.WriteLine(goodClarkGableFlick.Director);     // Victoria Fleming

About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

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