![]() With property delegation, the delegate is responsible for handling calls to the get and set functions of the property. Delegating propertiesīesides class delegation, you can also use the by keyword to delegate properties. This means you can easily switch the implementation without breaking the public API. Instead, it shares the same interface and decorates the internal object of the original type. With class delegation, your class is not part of any class hierarchy. The decorator class keeps an internal reference of the target class and wraps, or decorates, all the public methods provided with the interface.ĭelegates are especially useful when you can’t inherit from a particular class. In the decorator pattern, the decorator class shares the same interface with the class to be decorated. Note: The Kotlin compiler uses another design pattern called the Decorator Pattern to support class delegation in the generated code. When you use the by keyword, Kotlin automatically generates the code to use the innerList instance as a delegate. To do this, Kotlin introduces a new keyword: by. ![]() Kotlin provides a way to achieve this by delegating most of the work to an internal ArrayList instance and customizing its behavior. Wouldn’t be nice if you could override the remove() function to keep a reference of the deleted item and delegate the rest of the empty implementations of MutableList to some other object. Since this new class is extending the concrete ArrayList rather than implementing the MutableList interface, it is highly coupled with the concrete ArrayList implementation. One way to do this is to extend the ArrayList class. Basically, all you need is the same ArrayList functionality with a reference to the last removed item. Let’s say you have a use case for an ArrayList that can recover its last removed item. Kotlin makes delegation easier by providing support for class and property delegates and even containing some built-in delegates of its own. The delegate is responsible for handling the request on behalf of the original object and making the results available to the original object. Delegation is a design pattern in which an object handles a request by delegating to a helper object, called the delegate. ![]() Guess what, delegation is not new to software. No, I am not talking about delegating your work to your friend, but delegating work from one object to another. One way to get some work done is to delegate that work to another party.
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