Question

If I have a class

class widget {
    public int theNum;
    public string theName;
}

and I initalise like this

widget wgt = new widget { thename="tom" };

theNum will be zero.

Is there a way for me to examine the instance wgt to determine that the member theNum was defaulted i.e. excluded from the object initialisation?

Answer 1

As long as theNum is a field you cannot tell if it was left uninitialized or if it was explicitly initialized to its default value (which in this case is 0, but could be different if you had public int theNum = 42).

If theNum were a property then you could set a flag from within the property setter that allowed you to determine if the setter was invoked, no matter what value you set the property to. For example:

class widget {
    private int theNum;
    private bool theNumWasSet;
    public string theName;

    public int TheNum
    {
        get { return theNum; }
        set { theNumWasSet = true; theNum = value; }
    }
}