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Android Development with Kotlin

You're reading from   Android Development with Kotlin Enhance your skills for Android development using Kotlin

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Product type Paperback
Published in Aug 2017
Publisher Packt
ISBN-13 9781787123687
Length 440 pages
Edition 1st Edition
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Authors (2):
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Marcin Moskala Marcin Moskala
Author Profile Icon Marcin Moskala
Marcin Moskala
Igor Wojda Igor Wojda
Author Profile Icon Igor Wojda
Igor Wojda
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Table of Contents (10) Chapters Close

Preface 1. Beginning Your Kotlin Adventure FREE CHAPTER 2. Laying a Foundation 3. Playing with Functions 4. Classes and Objects 5. Functions as First-Class Citizens 6. Generics Are Your Friends 7. Extension Functions and Properties 8. Delegates 9. Making Your Marvel Gallery Application

Underscore for unused variables


In some cases, we define a lambda expression that does not use all its parameters. When we leave them named, they might be distracting to a programmer who is reading the lambda expression and trying to understand its purpose. Let's look at the function that filters every second element. The second parameter is the element value, and it is unused in this example:

    list.filterIndexed { index, value -> index % 2 == 0 } 

To prevent a misunderstanding, there are some conventions used, such as ignoring the parameter names:

    list.filterIndexed { index, ignored -> index % 2 == 0 } 

Because these conventions were unclear and problematic, Kotlin introduced underscore notation, which is used as a replacement for the names of parameters that are not used:

    list.filterIndexed { index, _ -> index % 2 == 0 } 

This notation is suggested, and there is a warning displayed when a lambda expression parameter is unused:

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