Service Consumers - Revision history

Alexander Kogtenkov: /* Using Consumers */ Removed unused local in code snippet.

2012-09-27T11:44:29Z

‎Using Consumers: Removed unused local in code snippet.

Paulb: Removed attachment marks

2009-04-03T23:48:00Z

Removed attachment marks

Paulb: Removed attachment marks from code examples, because this is not correct.

2008-10-29T17:05:34Z

Removed attachment marks from code examples, because this is not correct.

Paulb at 18:20, 11 June 2008

2008-06-11T18:20:36Z

Paulb: Corrected example code

2007-12-24T18:38:31Z

Corrected example code

Paulb: /* Services Are Tentative */

2007-12-12T01:30:40Z

‎Services Are Tentative

Paulb: Added page

2007-12-12T01:29:04Z

Added page

New page

[[Category:EiffelStudio Services]]
Services consumers are a simplest and safest means to use [[Griffin]]-based services from within [[EiffelStudio]].

== Services Are Tentative ==
Given the nature of [[Griffin]] services it is paramount that a service be checked for existence before attempting to use a service interface. Querying for a service is not guarentee to return a service even if it was available at some point. A service may have been available at the time of writing but it may not be available when a version of the [[EiffelStudio]] product is released. Many reasons exist for the tentative nature of a service, ranging from research, insufficient stability to meet the release deadline or deprecation. Building functionality around services should always respect the tentative nature and work to the best abilities, or restrict functionality, without the service in place. Service consumers can help.

== Using Consumers ==
The service consumer class ([https://svn.origo.ethz.ch/eiffelstudio/trunk/Src/framework/patterns/service_coupling/service_consumer.e SERVICE_CONSUMER] is generic and requires a generic parameter conforming SERVICE_I (base of all services). Once declared and instantiated the consumer may be used to query the service's existence and then access the service.

Below is a simple example of using the [[Session Manager Service]]:
<eiffel>
store_state
local
consumer: !SERVICE_CONSUMER [!SESSION_MANAGER_S]
service: !SESSION_MANAGER_S
do
create consumer
if consumer.is_service_available then
-- Service is available and can be used
consumer.service.retrieve (False) then
session.set_value (is_sorted, "com.eiffel.my_tool.sorted")
end
</eiffel>

=== Using Local Service Providers ===
Service consumers are used in place of using a service provider interface ([https://svn.origo.ethz.ch/eiffelstudio/trunk/Src/framework/patterns/service_coupling/service_provider.e SERVICE_PROVIDER]) directly, encapsulating the service and providing safe access to the service through a status function. Creating a service consumer using <eiffel>default_create</eiffel> as above will make use of the global service heap to fetch a service, based on [https://svn.origo.ethz.ch/eiffelstudio/trunk/Src/framework/patterns/service_coupling/service_consumer.e SERVICE_CONSUMER]'s generic parameter [https://svn.origo.ethz.ch/eiffelstudio/trunk/Src/Eiffel/API/framework/ecosystem/services/session/session_manager_s.e SESSION_MANAGER_S]. If a local service provider is available then creation of a service consumer should always use <eiffel>make_with_provider</eiffel> creation routine, because the local service provider may restrict or proffer services not available in the global service heap.

<eiffel>
service_provider: !SERVICE_PROVIDER
-- Local service provider

store_state
local
consumer: !SERVICE_CONSUMER [!SESSION_MANAGER_S]
do
-- Create service consumer with the local service provider of Current
create consumer.make_with_provider (service_provider)
if consumer.is_service_available then
...
end
end
</eiffel>

@@ Line 13: / Line 13: @@
    local
      consumer: SERVICE_CONSUMER [SESSION_MANAGER_S]
    do
      create consumer

@@ Line 12: / Line 12: @@
 store_state
    local
-     consumer: !SERVICE_CONSUMER [SESSION_MANAGER_S]
+     consumer: SERVICE_CONSUMER [SESSION_MANAGER_S]
      service: !SESSION_MANAGER_S
    do
@@ Line 18: / Line 18: @@
      if consumer.is_service_available then
          -- Service is available and can be used
-       if {session: !SESSION_I} consumer.service.retrieve (False) then
+       if attached {SESSION_I} consumer.service.retrieve (False) as session then
          session.set_value (is_sorted, "com.eiffel.my_tool.sorted")
        end
@@ Line 28: / Line 28: @@
 <eiffel>
-service_provider: !SERVICE_PROVIDER
+service_provider: SERVICE_PROVIDER
    -- Local service provider
 store_state
    local
-     consumer: !SERVICE_CONSUMER [SESSION_MANAGER_S]
+     consumer: SERVICE_CONSUMER [SESSION_MANAGER_S]
    do
        -- Create service consumer with the local service provider of Current

@@ Line 1: / Line 1: @@
 [[Category:EiffelStudio Services]]
-Services consumers are a simplest and safest means to use [[Griffin]]-based services from within [[EiffelStudio]].
+Services consumers are a simplest and safest means to use [[Griffin]]-based services from within [[:Category:EiffelStudio|EiffelStudio]].
 == Services Are Tentative ==
-Given the nature of [[Griffin]] services it is paramount that a service be checked for existence before attempting to use a service interface. Querying for a service is not guaranteed to return a service even if it was available at some point. A service may have been available at the time of writing but it may not be available when a version of the [[EiffelStudio]] product is released. Many reasons exist for the tentative nature of a service, ranging from research, insufficient stability to meet the release deadline or deprecation. Building functionality around services should always respect the tentative nature and work to the best abilities, or restrict functionality, without the service in place. Service consumers can help.
+Given the nature of [[Griffin]] services it is paramount that a service be checked for existence before attempting to use a service interface. Querying for a service is not guaranteed to return a service even if it was available at some point. A service may have been available at the time of writing but it may not be available when a version of the [[:Category:EiffelStudio|EiffelStudio]] product is released. Many reasons exist for the tentative nature of a service, ranging from research, insufficient stability to meet the release deadline or deprecation. Building functionality around services should always respect the tentative nature and work to the best abilities, or restrict functionality, without the service in place. Service consumers can help.
 == Using Consumers ==