Question

I have summarized my question in following code snippet

struct Point
{
    public int X;
    public int Y;

    public Point(int x, int y)
    {
        this.X = x;
        this.Y = y;
    }

    public override int GetHashCode()
    {
        return base.GetHashCode();
    }

    public void PrintValue()
    {
        Console.WriteLine(
            "{0},{1}",
            this.X, this.Y);
    }
}

above struct is derived from ValueType which contains GetHashCode method. Below is a class version which derives from Object and contains GetHashCode method.

class Point
{
    public int X;
    public int Y;

    public Point(int x, int y)
    {
        this.X = x;
        this.Y = y;
    }

    public override int GetHashCode()
    {
        return base.GetHashCode();
    }

    public void PrintValue()
    {
        Console.WriteLine(
            "{0},{1}",
            this.X, this.Y);
    }
}

I just wanted to know. Is there any difference between these implementations?

Answer 1

Yes; value-types (structs) by default make their hash-code as a composite of the values of their fields. You can observe this by trying:

var s = new Point(1,2); // struct
Console.WriteLine(s.GetHashCode());
s.X = 22; // <=============== struct fields should usually be readonly!
Console.WriteLine(s.GetHashCode()); // different

Note that Equals obeys similar rules.

By contrast, a reference-type (class) uses, by default, the reference itself for both GetHashCode() and Equals(). The s.X = 22 will not impact a class:

var s = new Point(1,2); // class
Console.WriteLine(s.GetHashCode());
s.X = 22;
Console.WriteLine(s.GetHashCode()); // same