16.4 Mapping for Interfaces

The server-side mapping for interfaces provides an up-call API for the Ice run time: by implementing methods in a servant class, you provide the hook that gets the thread of control from the Ice server-side run time into your application code.

16.4.1 Skeleton Classes

On the client side, interfaces map to proxy classes (see Section 5.12). On the server side, interfaces map to skeleton classes. A skeleton is a class that has an abstract method for each operation on the corresponding interface. For example, consider the Slice definition for the Node interface we defined in Chapter 5 once more:

module Filesystem {
    interface Node {
        idempotent string name();
    };
    // ...
};

The Slice compiler generates the following definition for this interface:

namespace Filesystem
{
    public interface NodeOperations_
    {
        string name(Ice.Current __current);
    }

    public interface NodeOperationsNC_
    {
        string name();
    }

    public interface Node : Ice.Object,
                            NodeOperations_, NodeOperationsNC_
    {
    }

    public abstract class NodeDisp_ : Ice.ObjectImpl, Node
    {
        public string name()
        {
            return name(new Ice.Current());
        }

        public abstract string name(Ice.Current __current);

        // Mapping‑internal code here...
    }
}

The important points to note here are:

• As for the client side, Slice modules are mapped to C# namespaces with the same name, so the skeleton class definitions are part of the Filesystem namespace.

• For each Slice interface <interface‑name>, the compiler generates C# interfaces <interface‑name>Operations_ and
<interface‑name>OperationsNC_ (NodeOperations_ and NodeOperationsNC_ in this example). These interfaces contain a method for each operation in the Slice interface. (You can ignore the Ice.Current parameter for the time being—we discuss it in detail in Section 32.6.)

• For each Slice interface <interface‑name>, the compiler generates a C# interface <interface‑name> (Node in this example). That interface extends Ice.Object and the two operations interfaces.

• For each Slice interface <interface‑name>, the compiler generates an abstract class <interface‑name>Disp_ (NodeDisp_ in this example). This abstract class is the actual skeleton class; it is the base class from which you derive your servant class.

16.4.2 Servant Classes

In order to provide an implementation for an Ice object, you must create a servant class that inherits from the corresponding skeleton class. For example, to create a servant for the Node interface, you could write:

public class NodeI : NodeDisp_
{
    public NodeI(string name)
    {
        _name = name;
    }

    public override string name(Ice.Current current)
    {
        return _name;
    }

    private string _name;
}

By convention, servant classes have the name of their interface with an I‑suffix, so the servant class for the Node interface is called NodeI. (This is a convention only: as far as the Ice run time is concerned, you can chose any name you prefer for your servant classes.) Note that NodeI extends NodeDisp_, that is, it derives from its skeleton class.

As far as Ice is concerned, the NodeI class must implement only a single method: the abstract name method that it inherits from its skeleton. This makes the servant class a concrete class that can be instantiated. You can add other methods and data members as you see fit to support your implementation. For example, in the preceding definition, we added a _name member and a constructor. (Obviously, the constructor initializes the _name member and the name method returns its value.)

Normal and idempotent Operations

Whether an operation is an ordinary operation or an idempotent operation has no influence on the way the operation is mapped. To illustrate this, consider the following interface:

interface Example {
   void              normalOp();
   idempotent void   idempotentOp();
};

The operations class for this interface looks like this:

public interface ExampleOperations_
{
    void normalOp(Ice.Current __current);
    void idempotentOp(Ice.Current __current);
}

Note that the signatures of the methods are unaffected by the idempotent qualifier.