Struct initialization and new operator

Question

I have two similar structs in C#, each one holds an integer, but the latter has get/set accessors implemented.

Why do I have to initialize the Y struct with

Answer 1

The reason one is valid while the other is not is that you cannot call methods on uninitialised objects. Property setters are methods too.

public struct X
{
    public int a;
    public void setA(int value)
    { this.a = value; }
}

public struct Y
{
    public int a { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        X x;
        x.setA(1); // A: error
        x.a = 2; // B: okay

        Y y;
        y.a = 3; // C: equivalent to A
    }
}

The reason that is not allowed is that the property setter could observe the uninitialised state of the object. The caller does not know whether the property setter merely sets a field, or does more than that.