C#

public struct Point
{

// _z will hold two flag bits to hold whether or not the values have been set
private int _x,_y,_z;

public int
x
{
    get
    {
        if ( _z%2 == 1 )
        {
            return ( _x ) ;
        }
        else
        {
            // throw something
        }
    }

    set
    {
        if ( _z%2 == 0 )
        {
            _x = value ;
            _z |= 1 ;
        }
        else
        {
            // throw something
        }
    }
}

public int
y
{
    get
    {
        if ( _z > 1 )
        {
            return ( _y ) ;
        }
        else
        {
            // throw something
        }
    }

    set
    {
        if ( _z < 2 )
        {
            _y = value ;
            _z |= 2 ;
        }
        else
        {
            // throw something
        }
    }
}

<br />
public Point my_Point;<br />
my_Point.x = 2;<br />
my_Point.y = 4;<br />
<br />
my_Point.x = 5; // The "throw something" will happen<br />

Luc Pattyn wrote:

You almost convinced me to embrace nullable types...

public struct Point
{


private int? _x,_y;

public int
x
{
    get
    {
        if ( _x.HasValue )
        {
            return ( _x.Value ) ;
        }
        else
        {
            // throw something
        }
    }

    set
    {
        if ( !_x.HasValue )
        {
            _x = value ;
        }
        else
        {
            // throw something
        }
    }
}

public int
y
{
    get
    {
        if ( _y.HasValue )
        {
            return ( _y.Value ) ;
        }
        else
        {
            // throw something
        }
    }

    set
    {
        if ( !_y.HasValue )
        {
            _y = value ;
        }
        else
        {
            // throw something
        }
    }
}

HashTable ht=new HashTable();
ht.Add("one", 1);
ht.Add("two", 2);
...

string s=myCombo.Text;    // if "two"
int myValue=(int)ht[s];   // then 2