The mapping of Slice interfaces revolves around the idea that, to invoke a remote operation, you call a member function on a local class instance that is a proxy for the remote object. This makes the mapping easy and intuitive to use because making a remote procedure call is no different from making a local procedure call (apart from error semantics).

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The Slice compiler generates the following definition for use by the client:

classdef SimplePrx < Ice.ObjectPrx
    methods
        function op(obj, varargin)
            ...
        end
    end
    methods(Static)
        function id = ice_staticId()
            ...
        end
        function r = checkedCast(proxy, varargin)
            ...
        end
        function r = uncheckedCast(proxy, varargin)
            ...
        end
    end
    ...
end

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An empty array denotes the null proxy. The null proxy is a dedicated value that indicates that a proxy points "nowhere" (denotes no object).

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Interface Inheritance in MATLAB

Inheritance relationships among Slice interfaces are maintained in the generated MATLAB classes. For example:

interface A { ... }
interface B { ... }
interface C extends A, B { ... }

The generated code for CPrx reflects the inheritance hierarchy:

classdef CPrx < APrx & BPrx
    ...
end

Given a proxy for C, a client can invoke any operation defined for interface C, as well as any operation inherited from C's base interfaces.

The ObjectPrx Interface in MATLAB

All Ice objects have Object as the ultimate ancestor type, so all proxies inherit from ObjectPrx.All Ice objects have Object as the ultimate ancestor type, so all proxies inherit from ObjectPrx. ObjectPrx provides a number of methods::

classdef ObjectPrx < handle
    methods
        function r = eq(obj, other)
        function r = ice_getIdentity(obj)
        function r = ice_isA(obj, id, varargin)
        function r = ice_ids(obj, varargin)
        function r = ice_id(obj, varargin)
        function ice_ping(obj, varargin)
        % ...
    end
end

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• ice_getIdentity
  This method returns the identity of the object denoted by the proxy. The identity of an Ice object has the following Slice type:

  Code Block
  language slice title Slice
  module Ice {     struct Identity {         string name;         string category;     } }

  To see whether two proxies denote the same object, first obtain the identity for each object and then compare the identities:

  Code Block
  language matlab title MATLAB
  proxy1 = ...; proxy2 = ...; id1 = proxy1.ice_getIdentity(); id2 = proxy2.ice_getIdentity(); if isequal(id1, id2)     % proxy1 and proxy2 denote the same object else     % proxy1 and proxy2 denote different objects end

• ice_isA
  The ice_isA method determines whether the object denoted by the proxy supports a specific interface. The argument to ice_isA is a type ID. For example, to see whether a proxy of type ObjectPrx denotes a Printer object, we can write:

  Code Block
  language matlab title MATLAB
  proxy = ...; if ~isempty(proxy) && proxy.ice_isA("::Printer")     % o denotes a Printer object else     % o denotes some other type of object end

  Note that we are testing whether the proxy is null before attempting to invoke the ice_isA method. This avoids getting an error if the proxy is an empty array.

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As we saw earlier, the Slice-to-MATLAB compiler generates static helper methods that support down-casting and type discovery:

classdef SimplePrx < Ice.ObjectPrx
    ...
    methods(Static)
        function id = ice_staticId()
            ...
        end
        function r = checkedCast(proxy, varargin)
            ...
        end
        function r = uncheckedCast(proxy, varargin)
            ...
        end
    end
    ...
end

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Given a proxy of any type, you can use a checkedCast to determine whether the corresponding object supports a given type, for example:

proxy = ...;        % Get a proxy from somewhere...

simple = SimplePrx.checkedCast(proxy);
if ~isempty(simple)
    % Object supports the Simple interface...
else
    % Object is not of type Simple...
end

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Suppose you expect to receive a proxy for a Process object and use an uncheckedCast to down-cast the proxy:

proxy = ...;                                % Get proxy...
process = ProcessPrx.uncheckedCast(proxy);  % No worries...
process.launch(40, 60);                     % Oops...

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The base proxy class ObjectPrx supports a variety of methods for customizing a proxy. Since proxies are immutable, each of these "factory methods" returns a copy of the original proxy that contains the desired modification. For example, you can obtain a proxy configured with a ten second invocation timeout as shown below:

proxy = communicator.stringToProxy(...);
proxy = proxy.ice_invocationTimeout(10000);

A factory method returns a new proxy object if the requested modification differs from the current proxy, otherwise it returns the current proxy. With few exceptions, factory methods return a proxy of the same type as the current proxy, therefore it is generally not necessary to repeat a checkedCast or uncheckedCast after using a factory method. Furthermore, the mapping generates type-specific factory methods so that no casts are necessary:

base = communicator.stringToProxy(...);
hello = HelloPrx.checkedCast(base);
hello = hello.ice_invocationTimeout(10000); % No cast is necessary
hello.sayHello();

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Proxies can be compared for equality using the == operator. Note that proxy comparison with == uses all of the information in a proxy for the comparison. This means that not only the object identity must match for a comparison to succeed, but other details inside the proxy, such as the protocol and endpoint information, must be the same. In other words, comparison with == tests for proxy identity, not object identity. A common mistake is to write code along the following lines:

proxy1 = ...;        % Get a proxy...
proxy2 = ...;        % Get another proxy...

if proxy1 == proxy2
    % proxy1 and proxy2 denote the same object         % Correct
else
    % proxy1 and proxy2 denote different objects       % WRONG!
end

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To compare the object identities of two proxies, you can use helper functions in the Ice package:

function r = proxyIdentityCompare(lhs, rhs)
function r = proxyIdentityAndFacetCompare(lhs, rhs)

proxyIdentityCompare allows you to correctly compare proxies for identity:

proxy1 = ...;        % Get a proxy...
proxy2 = ...;        % Get another proxy...

if Ice.proxyIdentityCompare(p1, p2) == 0
    % proxy1 and proxy2 denote the same object         % Correct
else
    % proxy1 and proxy2 denote different objects       % Correct
end

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• Interfaces, Operations, and Exceptions
• Proxies for Ice Objects
• Type IDs
• Request Contexts
• Operations on Object
• Proxy Methods
• Versioning