Client-Side Ruby Mapping for Interfaces

Proxy Classes

On the client side, a Slice interface maps to a Ruby class with methods that correspond to the operations on those interfaces. Consider the following Slice interface:

interface Simple
{
    void op();
}

The Ruby mapping generates the following definition for use by the client:

module SimplePrx_mixin
    def op(context=nil)
        ...
    end
end

class SimplePrx < Ice::ObjectPrx
    include SimplePrx_mixin
end

In the client's address space, an instance of SimplePrx is the local ambassador for a remote instance of an Ice object that implements Simple and is known as a proxy instance. All the details about the server-side object, such as its address, what protocol to use, and its object identity are encapsulated in that instance.

Creating a Proxy

Use the constructor of the generated class to create a proxy from a communicator and a “stringified” proxy. For example:

simple = M::SimplePrx.new(communicator, "simple:tcp -h localhost -p 4061")

Inheritance from Ice::ObjectPrx

All generated proxy classes inherit directly or indirectly from the Ice::ObjectPrx class, reflecting the fact that all Slice interfaces implicitly inherit from Object.

Interface Inheritance

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

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

The generated code for CPrx uses mixins to include the operations of APrx and BPrx:

module CPrx_mixin
    include APrx_mixin
    include BPrx_mixin
end

class CPrx < Ice::ObjectPrx
    include CPrx_mixin
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.

Casting a Proxy

All proxy classes provide 2 class methods that allow you to convert any proxy into a proxy of this type.

def uncheckedCast(proxy, facet: nil)
    ...
end

def checkedCast(proxy, facet: nil, context: nil)
   ...
end

uncheckedCast

The uncheckedCast method allows you to convert any proxy into a proxy of this type. For example:

# Convert a SimplePrx into a WidgetPrx, even though the two types are unrelated.
widget = M::WidgetPrx.uncheckedCast(simple)

uncheckedCast is a local operation that always succeeds.

checkedCast

checkedCastis a conditional cast of the proxy: this method makes a remote call to the target object to check if this object implements the proxy’s Slice interface. For example:

# Call operation ice_isA on the Ice object to check if it implements Slice interface
# Widget.
widget = M::WidgetPrx.checkedCast(simple)

If the target object implements the Slice interface, checkedCastreturns a new proxy, just like uncheckedCast. If the target object doesn’t implement this interface, checkedCast returns nil. checkedCastcan also throw an exception, for example if it cannot reach the remote object.

While checkedCast sounds safer than uncheckedCast (you’re making an additional check before casting), in practice you know or should know the type of your proxies and calling checkedCast is rarely necessary.

Proxy Factory Methods

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:

greeter = VisitorCenter::GreeterPrx.new(
    communicator,
    "greeter:tcp -h localhost -p 4061")

# Create a new GreeterPrx and assign it to greeter.
greeter = greeter.ice_invocationTimeout(10000)

The proxy factory methods usually return a proxy of the same type as the current proxy, like in the example above.

The only exceptions are the factory methods ice_facet and ice_identity. Calls to either of these methods may produce a proxy for an object of an unrelated type, and you need to cast the returned proxy. For example:

greeter = VisitorCenter::GreeterPrx.new(
    communicator, "greeter:tcp -h localhost -p 4061")
greeterAdmin = VisitorCenter::GreeterAdminPrx.uncheckedCast(
    greeter.ice_facet("admin"))