Generic Type constraint in .net
- by Jose
Okay I'm looking for some input, I'm pretty sure this is not currently supported in .NET 3.5 but here goes.
I want to require a generic type passed into my class to have a constructor like this:
new(IDictionary<string,object>)
so the class would look like this
public MyClass<T> where T : new(IDictionary<string,object>)
{
T CreateObject(IDictionary<string,object> values)
{
return new T(values);
}
}
But the compiler doesn't support this, it doesn't really know what I'm asking.
Some of you might ask, why do you want to do this? Well I'm working on a pet project of an ORM so I get values from the DB and then create the object and load the values.
I thought it would be cleaner to allow the object just create itself with the values I give it. As far as I can tell I have two options:
1) Use reflection(which I'm trying to avoid) to grab the PropertyInfo[] array and then use that to load the values.
2) require T to support an interface like so:
public interface ILoadValues
{
void LoadValues(IDictionary values);
}
and then do this
public MyClass<T> where T:new(),ILoadValues
{
T CreateObject(IDictionary<string,object> values)
{
T obj = new T();
obj.LoadValues(values);
return obj;
}
}
The problem I have with the interface I guess is philosophical, I don't really want to expose a public method for people to load the values. Using the constructor the idea was that if I had an object like this
namespace DataSource.Data
{
public class User
{
protected internal User(IDictionary<string,object> values)
{
//Initialize
}
}
}
As long as the MyClass<T> was in the same assembly the constructor would be available. I personally think that the Type constraint in my opinion should ask (Do I have access to this constructor? I do, great!)
Anyways any input is welcome.
