31 lines
1.4 KiB
Markdown
31 lines
1.4 KiB
Markdown
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---
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layout: pattern
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title: Role object
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folder: Migration
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permalink: /patterns/role-object/
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categories: Structural
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tags:
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- Java
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- Difficulty-Medium
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- Handle Body Pattern
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---
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## Also known as
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Post pattern, Extension Object pattern
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## Intent
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Adapt an object to different client’s needs through transparently attached role objects, each one representing a role
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the object has to play in that client’s context. The object manages its role set dynamically. By representing roles as
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individual objects, different contexts are kept separate and system configuration is simplified.
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## Applicability
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Use the Role Object pattern, if:
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- you want to handle a key abstraction in different contexts and you do not want to put the resulting context specific interfaces into the same class interface.
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- you want to handle the available roles dynamically so that they can be attached and removed on demand, that is at runtime, rather than fixing them statically at compile-time.
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- you want to treat the extensions transparently and need to preserve the logical object identity of the resultingobject conglomerate.
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- you want to keep role/client pairs independent from each other so that changes to a role do not affect clients that are not interested in that role.
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## Credits
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- [Hillside - Role object pattern](https://hillside.net/plop/plop97/Proceedings/riehle.pdf)
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- [Role object](http://wiki.c2.com/?RoleObject)
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- [Fowler - Dealing with roles](https://martinfowler.com/apsupp/roles.pdf)
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