C# How to declare a generic property with a constraint?

[eborman]

I'm trying to declare a property that is a generic and has a constraint and having no luck. Is it possible?

I want something like the following:

public interface IDeckPosition
{
...
}
 
public interface IRobotDeck
{
...
  Collection<T> Positions where T: IDeckPosition
}
 
 

[Shashi Sadasivan]

I'm trying to declare a property that is a generic and has a constraint and having no luck. Is it possible?

I want something like the following:

public interface IDeckPosition
{
...
}
 
public interface IRobotDeck
{
...
  Collection<T> Positions where T: IDeckPosition
}
 
 
 

What about

Collection<IDeckPosition> Positions;

[eborman]

The problem with that is that the following does not work:

public class RobotDeck : IRobotDeck
{
  private Collection<MyDeckPosition> _positions;
 
  public Collection<IDeckPosition> Positions
  { get return _positions;}
}
 

The above throws an error that there is no automatic conversion between the two collections.

[Plater]

Then cast it manually?
If MyDeckPosition inherits from the IDeckPosition class, you chould be able to cast it:

public class RobotDeck : IRobotDeck
{
  private Collection<MyDeckPosition> _positions;
 
  public Collection<IDeckPosition> Positions
  { 
    get
    { 
      return (Collection<IDeckPosition>)_positions;
    }
}
 

The rules for casting T type collections might be different, but I'm fairly certain it can be done.

[r035198x]

The problem with that is that the following does not work:

public class RobotDeck : IRobotDeck
{
  private Collection<MyDeckPosition> _positions;
 
  public Collection<IDeckPosition> Positions
  { get return _positions;}
}
 

The above throws an error that there is no automatic conversion between the two collections.

I think your problem is that you are trying to declare an attribute in an interface.
Interfaces can contain properties along with Events, methods and indexers but they cannot contain attributes.

[eborman]

I get the same error "cannot convert type x to type y via built in conversion" whether the conversion is automatic or manual.

[Plater]

Does MyDeckPosition inherit/implement from the IDeckPosition interface?
Actually, why not just use the Strong type instead of the interface to begin with?

[eborman]

I think your problem is that you are trying to declare an attribute in an interface.
Interfaces can contain properties along with Events, methods and indexers but they cannot contain attributes.

It's definitely not an attribute.

[r035198x]

It's definitely not an attribute.

What then do you call it? I'm talking about the Positions "attribute" in the IRobotDeck interface It not a property, event, method or indexer.
... and those are the only things you can declare inside an interface.

[eborman]

Does MyDeckPosition inherit/implement from the IDeckPosition interface?

Yes, It inherits from the interface.

Actually, why not just use the Strong type instead of the interface to begin with?

I have a visual control that I'll use to display the RobotDeck. This control will be in a different assembly, our controls assembly. I did not want to introduce a dependency to our manufacturing assembly.

I may just break out that control into its own assembly and live with the dependency.

[eborman]

What then do you call it? I'm talking about the Positions "attribute" in the IRobotDeck interface It not a property, event, method or indexer.
... and those are the only things you can declare inside an interface.

Sorry. I forgot to add the getter. Does the following make it clearer:

public interface IRobotDeck
{
..
  Collection<T> Positions where T: IDeckPosition {get;}
  int MyProperty {get;}
}
 

[r035198x]

Yes, It inherits from the interface.



I have a visual control that I'll use to display the RobotDeck. This control will be in a different assembly, our controls assembly. I did not want to introduce a dependency to our manufacturing assembly.

I may just break out that control into its own assembly and live with the dependency.

Shouldn't it be like

interface IRobotDeck {
          Collection<IDeckPosition> Positions {
                 get;
                 set;
          }
}

[Plater]

Shouldn't it be like

interface IRobotDeck {
          Collection<IDeckPosition> Positions {
                 get;
                 set;
          }
}

Only if you want the object exposed by Positions to be writeable(changable, for things like a collection, you can still .Add()/.Remove() on a GET only property). Read-only properties would only contain the get right?

[eborman]

Only if you want the object exposed by Positions to be writeable(changable, for things like a collection, you can still .Add()/.Remove() on a GET only property). Read-only properties would only contain the get right?

Correct, specifying teh getter means that it is read only. Which is what I want.

[r035198x]

Correct, specifying teh getter means that it is read only. Which is what I want.

So you are still getting the conversion error thing? Why don't you post all your class definitions.

[eborman]

So you are still getting the conversion error thing? Why don't you post all your class definitions.

Sorry about the late response, I got tied up with a couple of other things. I think that I'm going to go with two collections one with the actual objects and then the other will contain the interfaces for the objects. Syncing shouldn't be a problem as the list will be static.

[KiwiHawk]

public interface IRobotDeck<T> where T : IDeckPosition
{
Collection<T> Positions {
get;
set;
}
}