Operations on Object

The Object interface has a number of operations. We cannot define type Object in Slice because Object is a keyword; regardless, here is what (part of) the definition of Object would look like if it were legal:

sequence<string> StrSeq;

interface Object                      // "Pseudo" Slice!
    idempotent void   ice_ping();
    idempotent bool   ice_isA(string typeID);
    idempotent string ice_id();
    idempotent StrSeq ice_ids();
    // ...

Note that, apart from the illegal use of the keyword Object as the interface name, the operation names all contain the ice_ prefix. This prefix is reserved for use by Ice and cannot clash with a user-defined operation. This means that all Slice interfaces can inherit from Object without name clashes. We discuss these built-in operations below.

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All interfaces support the ice_ping operation. That operation is useful for debugging because it provides a basic reachability test for an object: if the object exists and a message can successfully be dispatched to the object, ice_ping simply returns without error. If the object cannot be reached or does not exist, ice_ping throws a run-time exception that provides the reason for the failure.


The ice_isA operation accepts a type identifier (such as the identifier returned by ice_id) and tests whether the target object supports the specified type, returning true if it does. You can use this operation to check whether a target object supports a particular type. For example, referring to the diagram Implicit Inheritance from Object once more, assume that you are holding a proxy to a target object of type AlarmClock. The table below illustrates the result of calling ice_isA on that proxy with various arguments. (We assume that all types in the Implicit inheritance from Object diagram are defined in a module Times):













Calling ice_isA on a proxy denoting an object of type AlarmClock.

As expected, ice_isA returns true for ::Times::Clock and ::Times::AlarmClock and also returns true for ::Ice::Object (because all interfaces support that type). Obviously, an AlarmClock supports neither the Radio nor the RadioClock interfaces, so ice_isA returns false for these types.


The ice_id operation returns the type ID of the most-derived type of an interface.


The ice_ids operation returns a sequence of type IDs that contains all of the type IDs supported by an interface. For example, for the RadioClock interface in Implicit inheritance from Object, ice_ids returns a sequence containing the type IDs ::Ice::Object, ::Times::Clock, ::Times::AlarmClock, ::Times::Radio, and ::Times::RadioClock.

See Also