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    <p>At first glance this calls for the <a href="http://en.wikipedia.org/wiki/Strategy_pattern" rel="nofollow noreferrer">Strategy pattern</a> (or in fact <a href="http://en.wikipedia.org/wiki/Template_method_pattern" rel="nofollow noreferrer">Template Method</a>), possibly with a <a href="http://en.wikipedia.org/wiki/Factory_method_pattern" rel="nofollow noreferrer">Factory Method</a> to control which strategy to use. Example (in pseudo-Java):</p> <pre><code>class Saver { protected void LegacySave(Employee e) {} public final void Save(Employee e) { NewSystemEmployee.Save(e); LegacySave(e); } } class LegacySaver extends Saver { protected void LegacySave(Employee e) { LegacySystemEmployee.Save(e); } } </code></pre> <p>Since at some point in time you will no more need the legacy call, it makes sense to implement the default <code>LegacySave</code> as empty. Then you can trivially use the class like this:</p> <pre><code>getSaver().save(employee); </code></pre> <p>where <code>getSaver()</code> is the factory method which silently decides which <code>Saver</code> implementation to present to its caller. Trivially it can get the class name from a config file.</p> <p>Question is, how do you need to change the behaviour: runtime, or by restarting the application? If you can restart the application, it is easy to change that one line in the configuration which controls the strategy to use. Changing behaviour on-the-fly is slightly more tricky, but doable.</p> <p>A lot depends on what programming language you use. E.g. in Java / C++ / C# you can easily accomplish what you want with <a href="http://en.wikipedia.org/wiki/Dependency_injection" rel="nofollow noreferrer">dependency injection</a>; in some other languages it might not be that easy.</p>
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    1. COChain of Responsiblity or Strategy would work here.
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    2. COYes, I plan re starting the application.
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    3. COPeter, this looks like a very good way to implement what I need. I have a slightly different way to do this. The code below is c# <pre> class Saver { public void Save(Employee e) { NewSystemEmployee.Save(e); } } class LegacySaver : Saver { public void Save(Employee e) { base.Save(e); // NewSystemEmployee LegacySystemEmployee(e); } } The factory would still determine which Saver implementation to use. I was wondering what you thought of the method I came up with? Do you see any problems? Thanks
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