如何使用模板委托

Question

I'm trying to use a templated delegate in one of my class.

Here the class definition :

internal class MyClass : BaseClass
{
    public delegate T Create<T>(int identity) where T : SomeOtherClass;
    public Create<T> CreateCB {get;set;}    //<-- This here doesn't compile
}

I will use the CreateCB such as this

return CreateCB<InheritedClassFromSomeOtherClass>(someId);

and

return CreateCB<OtherInheritedClassFromSomeOtherClass>(someId);

etc.

I can't template the whole MyClass since it will need to use the delegate to create many different type who inherit from SomeOtherClass

The line who doesn't compile don't need to be a property but I still need to use my generic templated delegate. How can I do this?

My app target .net 4 client profile

Answer 1

Your T is scoped to the delegate, but the T you're trying to use in the property is undefined.

Your problem here is that there is no such thing as a generic property, therefore you can't define T .

There are two workarounds:

• Make the class generic, so T is defined everywhere:

   internal class MyClass<T> : BaseClass where T : SomeOtherClass { public delegate T Create(int identity); // Now T is in scope public Create CreateCB { get; set; } } 

• Use a getter/setter pair, if you really can't make the class generic, but this is... ugly :

   internal class MyClass : BaseClass { private object _createCB; public delegate T Create<T>(int identity) where T : SomeOtherClass; public Create<T> GetCreateCB<T>() where T : SomeOtherClass; { return (Create<T>)_createCB; } public void SetCreateCB<T>(Create<T> fn) where T : SomeOtherClass; { _createCB = fn; } } 

  Hopefully this snippet shows why there's no such thing as a generic property in the first place. You lose the strong typing anyway because of the storage. And you have to provide T explicitly on each get/set - you'd better be coherent with that.