C#

[StructLayout( LayoutKind.Explicit )]
public struct Number
{
	private enum NumType
	{
		Double,
		Int64
	}

	[FieldOffset( 0 )]
	double dblValue;
	[FieldOffset( 0 )]
	long lngValue;
        [FieldOffset( 8 )]
	NumType type;

        public void Set( double value )
	{
		type = NumType.Double;
		dblValue = value;
	}
	public void Set( long value )
	{
		type = NumType.Int64;
		lngValue = value;
	}

	public double GetDouble()
	{
		if ( type == NumType.Double )
		{
			return dblValue;
		}
		return (double)lngValue;
	}
	public long GetLong()
	{
		if ( type == NumType.Int64 )
		{
			return lngValue;
		}
		return (long)dblValue;
	}
}