[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: What is delegation
Dean Roddey wrote: > > I'm sure you'll get some definitions, but here are > some examples that may help... See also my response of this morning, archived at http://www.lists.ic.ac.uk/hypermail/xml-dev/9810/0245.html Some technical motivations for delegating: - Coping with situations where the interface isn't "exactly" the same (e.g. adapters that implicitly add another argument, extra setup needed, etc); - Sometimes you need lots of objects to delegate to the same object, and yet have distinct identity. That object might be a flyweight, but to use it in some cases you might need to restore its weight. - Base classes differ; client A needs something to call object B but needs its callback to derive from some concrete class. It delegates to object C which is so derived, and which calls B. - As Dean noted, "composite" objects include others with "has-a". Distributed systems often work that way ... a user account object "has-a" home directory, a password, a set of files. But those are objects in their own right, so "is-a" (subtyping) is wrong. I've not found "aggregation" to be helpful except when talking about COM, but that may be because COM has rules about aggregating that don't apply to more classic object composition/delegation schemes. And of course, everyone has their own ways to slice'n'dice design problems. - Dave xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
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