Скачать или смотреть Creating a Flexible Lambda in Kotlin: How to Return Each Internal Object Efficiently

Discover how to elegantly create a custom lambda expression in Kotlin that allows you to minimize code duplication while iterating over a list of objects.
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Creating a Flexible Lambda in Kotlin

Kotlin’s lambda expressions empower developers to write concise and efficient code. One common desire is to create a lambda that operates similarly to the built-in forEach function but with the flexibility to call different methods on wrapped objects. If you've ever faced a situation where you needed to iterate through a list of objects, wrap each object, and call a specific method on the wrapper, this guide is for you.

The Scenario

Imagine having a class called Action with a list of objects that you want to process. For each object, you wrap it in an instance of a Wrapper class and perform some actions. Here's how this might look:

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At this point, you're well on your way to performing your intended actions. However, you quickly realize you need to replicate this structure for another method, runB, leading to code duplication. The question then arises: How can you refactor this in Kotlin elegantly while minimizing duplicated code?

The Problem

You want to create a method called runB without rewriting the code for creating the Wrapper each time. You also cannot directly pass a method as a parameter because the wrapper instance is generated inside the forEach loop, limiting your ability to easily reference it.

Here’s what your current setup looks like:

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The Solution

To tackle this, you can enhance your runMethod function by adding a receiver to the lambda. This means that the Wrapper instance will be treated as this within the lambda passed to runMethod(). By doing so, you can seamlessly call methods on the Wrapper without the need for redundancy.

Here’s how you might implement this solution:

Updated runMethod

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Utilizing the Enhanced runMethod

Now, you can define your runA and runB methods without redundancy, like so:

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Shorter Notation

You can even use Kotlin’s function reference feature for a more concise approach:

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Conclusion

By introducing a receiver into your lambda expressions, you can elegantly and efficiently manage similar operations on wrapped objects in Kotlin. This strategy not only reduces code duplication but also improves readability, maintaining the clarity and intention behind your method calls. So the next time you find yourself writing redundant loops, remember this powerful technique!

Happy coding with Kotlin!