Convert base class to derived class [duplicate]

Question

Is it possible in C# to explicitly convert a base class object to one of it's derived classes? Currently thinking I have to create a constructor for my derived classes that accept a base class object as a parameter and copy over the property values. I don't really like this idea, so I'd like to avoid it if possible.

This doesn't seem like it should work (object is instantiated as new base, so memory shouldn't be allocated for extra members of the derived class) but C# seems to allow me to do it:

class BaseClass {   ... some stuff ... }  class DerivedClass : BaseClass {     public bool MyDerivedProperty{ get; set; } }   static void Main(string[] args) {     BaseClass myBaseObject = new BaseClass();     DerivedClass myDerivedObject = myBaseObject as DerivedClass;      myDerivedObject.MyDerivedProperty = true; } 

Answer 1

No, there's no built-in way to convert a class like you say. The simplest way to do this would be to do what you suggested: create a DerivedClass(BaseClass) constructor. Other options would basically come out to automate the copying of properties from the base to the derived instance, e.g. using reflection.

The code you posted using as will compile, as I'm sure you've seen, but will throw a null reference exception when you run it, because myBaseObject as DerivedClass will evaluate to null, since it's not an instance of DerivedClass.

Answer 2

That's not possible. but you can use an Object Mapper like AutoMapper

EDIT

I want to suggest a simpler object mapper: TinyMapper. AutoMapper is now very complicated to use. I don't use it anymore. TinyMapper covers most use cases and is far more simple AND super fast.

Example:

//In app startup TinyMapper.Bind<Person, PersonDto>();  //Usage var personDto = TinyMapper.Map<PersonDto>(person); 

---

Example for AutoMapper (older versions I think) for the ones who still want to use it:

class A {     public int IntProp { get; set; } } class B {     public int IntProp { get; set; }     public string StrProp { get; set; } } 

In global.asax or application startup:

AutoMapper.Mapper.CreateMap<A, B>(); 

Usage:

var b = AutoMapper.Mapper.Map<B>(a); 

It's configurable via a fluent API.