Daniel Boelzle schrieb:
-4- TypeDescriptionProvider / TypeDescriptionManager: Services providing
access to type descriptions. The TypeDescriptionManager just delegates
requests to the registered providers. The returned type descriptions are
different of what the CoreReflection provides and are for informational
purposes only. E.g. the remote bridges use these type descriptions.
Singletons, as the TypeDescriptionManager, can either be retrieved via
the "createInstance" method of the ServiceManager (which returns the
same object all the same, in case it is a singleton), or via the
No, this is wrong. The service manager's createInstance...() methods
semantically always create new objects. If objects are implemented
stateless, you may get the very same instance again, because the
implementor decided to safely do so. IMO Kay thinks of old
"OneInstanceFactory" implementations, which are not stateless. Due to
this mix-up, that concept is considered to be deprecated. The
distinction between singletons and multi-instance is clear:
- a singleton instance is accessed via component context
- a service instance is created via service manager
Singletons, as "/singletons/...theTypeDescriptionManager" can only be
retrieved via the component context, a createInstance call at the
service manager will return a new (uninitialized) one.
I've difficulties with this thinking. The structure of an object
is always defined - regardless of a context. The initialization
may be not possible without an context - but the structure should
be always there.
And the questions are still the same:
- WHAT is a usable context of theTypeDescriptionManager ?
- How do I get the singleton of theTypeDescriptionManager ?
And if one have 6 different ways to get different meta information
about objects I would ask myself: why ?
And if I read:
>-6- XServiceInfo: An interface providing the implementation name and the
>supported services of an object. This was/is needed for objects not
>implemented using the new multiple inheritance stuff.
the next question comes to my mind: how do I get the information
if one service is using the "multiple inhertitance" stuff.
Actually I thought, that the whole stuff is easy:
- Interfaces have methods, properties, structs, enumerations, exceptions
- Services can support multiple interfaces
- Singletons are instances of Services, which should only
exists once.
Marten
--
Marten Feldtmann - Germany - Software Development
Information regarding VA Smalltalk and DMS-system
"MSK - Mien Schrievkrom" at: www.schrievkrom.de
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