系统结构/类的自动可为空的转换操作符

Question

I am attempting to convert a huge project away from using XSD's to using entities, but a problem with this is that XSD's did not generate Nullable types, they generated non-nullable types and generated methods such as IsMyFieldNameNull() .

I would like to have our entities work properly and be nullable types, but i would not like to go round the (400,000 SLOC) project and add .Value to all instance of every access to an entity property.

I came up with:

namespace System
{
    public partial struct Int64
    {
        public static explicit operator Int64(Int64? d)
        {
            return (d.Value);
        }
    }
}

But am being given the error "Conversion operator with same parameter and return types". Does anybody know how to best work around this, and if the code above is even possible?

Answer 1

To resolve this, maintain backwards compatibility with existing code, good practice with future code. I came up with the following code:

public class Auto<T> where T: struct
{
    private T? _value;

    public Auto()
    {
        _value = default(T);
    }

    public Auto(T val)
    {
        _value = val;
    }

    public Auto(T? val)
    {
        _value = val;
    }

    public bool HasValue
    {
        get
        {
            return _value.HasValue;
        }
    }

    public T Value
    {
        get { return _value.HasValue ? _value.Value : default(T); }
    }

    public static implicit operator T(Auto<T> d)
    {
        return d._value.HasValue ? d._value.Value : default(T);
    }

    public static implicit operator Auto<T>(T d)
    {
        return new Auto<T>(d);
    }

    public static implicit operator T?(Auto<T> d)
    {
        return (d._value);
    }

    public static implicit operator Auto<T>(T? d)
    {
        return new Auto<T>(d);
    }
}

To be used:

class MyEntity
{
    public Auto<long> ID;
    public Auto<short> Status;
    public String Name;

   //rest of entity code here
}

This way, i do not have to go around the existing code base adding .HasValue 's and .Values everywhere, and i also dont have to use IsStatusNull() (though these methods are required for compatibility reasons, they will simply return HasValue ).

Not sure how helpful this would be to others, but this is the most sensible way of creating my new DAL layer to replace my old bad DAL layer, and having to change as little as possible in the existing BLL and App layers.