如何在运行时创建子类以映射某些属性，然后将其强制转换回父类？

Question

Consider this People class:

public class People
{
    public virtual string Name { get; set; }    
    public virtual ushort Age { get; set; }
}

I have some third party implementations that can obtain people data but with a little variations. For example, I have a method that is able to retrieve data for StrangePeople :

    public class StrangePeople
    {
        public string Name { get; set; }        
        public DateTime BirthDate { get; set; }
    }
    ...
    StrangePeople someone = GetData<StrangePeople>();

Due to the amount of classes and variations I trying to found a way to generate a runtime subclass of People that can translate the data so I can cast it back to People later. In other words, with minimum effort generate a subclass like this:

public class StrangePeopleTranslator : People
{
    private ushort? _mAge = null;

    public override ushort Age
    {
        get
        {
            if (_mAge == null)
            {
                DateTime today = DateTime.Today;
                int age = today.Year - BirthDate.Year;
                if (BirthDate > today.AddYears(-age)) age--;
                _mAge = age;
            }

            return _mAge.GetValueOrDefault();
        }
        set
        {
            _mAge = value;
        }
    }

    public DateTime BirthDate { get; set; }
}

...

People someoneElse = (People)GetData<StrangePeopleTranslator>();

Maybe the run-time subclass it's bit overkill... I don't know.

Answer 1

The best thing you can do is provide an implicit cast overload. That way you can convert from StrangePeople to People , like this:

public class StrangePeople
{
    public string Name { get; set; }
    public DateTime BirthDate { get; set; }

    public static implicit operator People(StrangePeople strangePerson)
    {
        DateTime today = DateTime.Today;
        int age = today.Year - strangePerson.BirthDate.Year;
        if (strangePerson.BirthDate > today.AddYears(-age))
        {
            age--;
        }

        return new People
                    {
                        Name = strangePerson.Name,
                        Age = (ushort) age
                    };
    }

Then you could do this:

People someoneElse = GetData<StrangePeopleTranslator>();

You don't even need a cast.

Answer 2

Well, depending on how much effort you're willing to put in to this, you could use a single subclass with dynamically generated Func s using System.Linq.Expressions. You'll need to be using C#4 for full functionality here.

The basic idea:

public class Subclass : People
{
    public Func<DateTime, ushort> BirthDateToAge;
    ushort _mAge;

    public override ushort Age
    {
        get { return AgeImpl(_mAge); }
        set { _mAge = value; }
    }
}

// And then somewhere else where you'd want to create the "subclass"
var people = new Subclass();
Func<DateTime, ushort> setter = (Func<DateTime, ushort>)(bday => (ushort)CalcElapsedYears(bday));
people.AgeImpl = setter;

You'll probably need to factor it differently, but the basic concept is the same: create a generic subclass that can operate entirely via Func<> s, and then build those Func<> s when you do your reflection or whatnot.

It's kind harebrained, but it should work.