Create a decorator

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For more information on the decorator pattern, check out this Wikipedia article.

The Decorator design pattern is used to dynamically add additional behavior to an object. In addition, by using interfaces, a decorator can be used to unify types in a manner similar to multiple inheritance.

Let’s take an example – suppose you have two objects, called Bird and Lizard, that you want to put into a Decorator:


Get object interfaces with the extract interface refactoring

Since a decorator cannot be inheriting from both of these classes, we can use the Extract Interface in-place refactoring (Ctrl+Shift+R) for both of these objects to get their interfaces:

Calling this refactoring pops up a window asking us which members should appear in the interface:

After we do this for both our classes, we end up with the following code:

Declare a decorator class

With these interfaces, we can make a decorator. First, we declare a class called Dragon, indicating that it implements both IBird and ILizard:

Now for the aggregated members. The easiest thing to do is to declare both of these as fields first, i.e.:

Use quick-fix to initialize unused fields

Now, we can use ReSharper to initialize both of these fields from constructor parameters:

After this, our class will look as follows:

Generate delegating members for source objects.

And now for the finishing touch – we want to generate delegating members for both bird and lizard. This is easy – we simply open the Generate menu and choose Delegating Members:

ReSharper then asks us which members we need to delegate:

And here is the end result:

That’s it! Our decorator is ready.

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