How to use method hiding (new) with generic constrained class
- by ongle
I have a container class that has a generic parameter which is constrained to some base class. The type supplied to the generic is a sub of the base class constraint. The sub class uses method hiding (new) to change the behavior of a method from the base class (no, I can't make it virtual as it is not my code). My problem is that the 'new' methods do not get called, the compiler seems to consider the supplied type to be the base class, not the sub, as if I had upcast it to the base.
Clearly I am misunderstanding something fundamental here. I thought that the generic where T: xxx was a constraint, not an upcast type.
This sample code basically demonstrates what I'm talking about.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace GenericPartialTest
{
class ContextBase
{
public string GetValue()
{
return "I am Context Base: " + this.GetType().Name;
}
public string GetOtherValue()
{
return "I am Context Base: " + this.GetType().Name;
}
}
partial class ContextSub : ContextBase
{
public new string GetValue()
{
return "I am Context Sub: " + this.GetType().Name;
}
}
partial class ContextSub
{
public new string GetOtherValue()
{
return "I am Context Sub: " + this.GetType().Name;
}
}
class Container<T> where T: ContextBase, new()
{
private T _context = new T();
public string GetValue()
{
return this._context.GetValue();
}
public string GetOtherValue()
{
return this._context.GetOtherValue();
}
}
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Simple");
ContextBase myBase = new ContextBase();
ContextSub mySub = new ContextSub();
Console.WriteLine(myBase.GetValue());
Console.WriteLine(myBase.GetOtherValue());
Console.WriteLine(mySub.GetValue());
Console.WriteLine(mySub.GetOtherValue());
Console.WriteLine("Generic Container");
Container<ContextBase> myContainerBase = new Container<ContextBase>();
Container<ContextSub> myContainerSub = new Container<ContextSub>();
Console.WriteLine(myContainerBase.GetValue());
Console.WriteLine(myContainerBase.GetOtherValue());
Console.WriteLine(myContainerSub.GetValue());
Console.WriteLine(myContainerSub.GetOtherValue());
Console.ReadKey();
}
}
}
