Thanks for purchasing the MEAP for Kotlin in Action! Kotlin in Action MEAP V11 - … Kotlin in Action guides experienced Java developers from the language basics of Kotlin all the way through building applications to run on the JVM and Android devices. 8 Higher-Order Functions: Lambdas as Parameters and Return Values. And with an efficient compiler and a small standard library, Kotlin imposes virtually no runtime overhead. Reason. Article: Compiler-generated Methods: data classes and class delegation, Article: Declaring Higher-order Functions. Kotlin can be compiled to Java bytecode, so you can use it everywhere Java is used, including Android. The Kotlin programming language offers an expressive syntax, a strong intuitive type system, and great tooling support along with seamless interoperability with existing Java code, libraries, and frameworks. Written for experienced Java developers, this example-rich book goes further than most language books, covering interesting topics like building DSLs with natural language syntax. 3 Defining and Calling Functions. Report "Kotlin in Action v12 MEAP" Please fill this form, we will try to respond as soon as possible. First, conciseness Functional code can be more elegant and succinct compared to its imperative counterpart, because working with functions as values gives you much more power of abstraction, which lets you avoid duplication in your code Imagine that you have two similar code fragments that implement a similar task (for example, looking for a matching element in a collection) but differ in the details (how the matching element is detected) You can easily extract the common part of the logic into a function and pass the differing parts as parameters Those parameters are themselves functions, but you can express them using a concise syntax for anonymous functions called lambda expressions: fun findAlice() = findPerson { == "Alice" } fun findBob() = findPerson { == "Bob" } findPerson() contains the general logic of finding a person The block in curly braces identifies the specific person you need to find The second benefit of functional code is safe multithreading One of the biggest sources of errors in multithreaded programs is modification of the same data from multiple threads without proper synchronization If you use immutable data structures and pure functions, you can be sure that such unsafe modifications won’t happen, and you don’t need to come up with complicated synchronization schemes Finally, functional programming means easier testing Code without side effects is usually easier to test Functions can be tested in isolation without requiring a lot of setup code to construct the entire environment that they depend on Generally speaking, the functional style can be used with any programming language, including Java, and many parts of it are advocated as good programming style But not all languages provide the syntactic and library support required to use it effortlessly; for example, this support was mostly missing from versions of Java before Java Kotlin has a rich set of features to support functional programming from the get-go These include the following: Functional types, allowing functions to receive other functions as parameters or return other functions Lambda expressions, letting you pass around blocks of code with minimum boilerplate Data classes, providing a concise syntax for creating immutable value objects A rich set of APIs in the standard library for working with objects and collections in the functional style Kotlin lets you program in the functional style but doesn’t enforce it When you need it, you can work with mutable data and write functions that have side effects without jumping through any extra hoops And, of course, working with frameworks that are based on interfaces and class hierarchies is just as easy as with Java When writing code in Kotlin, you can combine both the object-oriented and functional approaches and use the tools that are most appropriate for the problem you’re solving taking "USA" as an argument, and you can correctly guess that it’s another member extension Here we again come across an extension method on Column that is also a member and thus can be used only in the appropriate context, for instance when specifying the condition of the select method The simplified declarations of the select and eq methods are below: fun SqlExpressionBuilder. With Kotlin, you can implement your projectswithlesscode,ahigherlevelofabstraction,andfewer annoyances. Your name. Kotlin can be compiled to Java bytecode, so you can use it everywhere Java is used, including Android. FREE domestic shipping on three or more pBooks. The first one is the third argument of the alert function The other two lambdas are passed as arguments to positiveButton and negativeButton The receiver of the first (outer) lambda has the type AlertDialogBuilder The same pattern comes up again: the name of the AlertDialogBuilder class won’t appear in the code directly, but you can access its members to add elements to the alert dialog The declarations of the members used in the example are shown below: fun Context.alert( message: String, title: String, init: AlertDialogBuilder. We're looking forward to introducingyoutoKotlin,whichisanewprogram minglanguagethatisapragmatic,safe, concise, and interoperable alternative to Java. This book is for experienced Java developers. purchasing the MEAP for Kotlin in Action! + liveBook, 3 formats Thanks for purchasing the MEAP for Kotlin in Action! Read on to learn more and become a Kotlin expert We hope that soon you’ll see such code in your own projects, not only in this book 1.2 Kotlin’s primary traits You probably already have an idea what kind of language Kotlin is Let’s look at its key attributes in more detail First of all, let’s see what kinds of applications you can build with Kotlin 1.2.1 Target platforms: server-side, Android, anywhere Java runs The primary goal of Kotlin is to provide a more concise, more productive, safer alternative to Java that’s suitable in all contexts where Java is used today Java is an extremely popular language, and it’s used in a broad variety of environments, from smart cards (Java Card technology) to the largest data centers run by Google, Twitter, LinkedIn, and other internet-scale companies In most of these places, using Kotlin can help developers achieve their goals with less code and fewer annoyances along the way The most common areas to use Kotlin are these: Building server-side code (typically, backends of web applications) Building mobile applications that run on Android devices But Kotlin works in other contexts as well For example, you can use the Intel MultiOS Engine to run Kotlin code on iOS devices To build desktop applications, you can use Kotlin together with JavaFX Footnote Footnote "JavaFX: Getting Started with JavaFX," Oracle, In addition to Java, Kotlin can also be compiled to JavaScript, allowing you to run Kotlin code in the browser But as of this writing, JavaScript support is still being explored and prototyped at JetBrains, so it’s out of scope for this book Other platforms are also under consideration for future versions of the language As you can see, Kotlin’s target is quite broad Kotlin doesn’t focus on a single problem domain or address a single type of challenge faced by software developers today Instead, it provides across-the-board productivity improvements for all tasks that come up during the development process It gives you an excellent level of integration with libraries that support specific domains or programming paradigms Let’s look next at the key qualities of Kotlin as a programming language 1.2.2 Statically typed Just like Java, Kotlin is a statically typed programming language This means the type of every expression in a program is known at compile time, and the compiler can validate that the methods and fields you’re trying to access exist on the objects you’re using This is in contrast to dynamically typed programming languages, which are represented on the JVM by, among others, Groovy and JRuby Those languages let you define variables and functions that can store or return data of any type and resolve the method and field references at runtime This allows for shorter code and greater flexibility in creating data structures But the downside is that problems like misspelled names can’t be detected during compilation and lead to runtime errors On the other hand, in contrast to Java, Kotlin doesn’t require you to specify the type of every variable explicitly in your source code In many cases, the type of a variable can automatically be determined from the context, allowing you to omit the type declaration Here’s the simplest possible example of this: val x = You’re declaring a variable, and because it’s initialized with an integer value, Kotlin automatically determines that its type is Int The ability of the compiler to determine types from context is called type inference Following are some of the benefits of static typing: Performance - Calling methods is faster because there’s no need to figure out at runtime which method needs to be called Reliability - The compiler verifies the correctness of the program, so there are fewer chances for crashes at runtime Maintainability - Working with unfamiliar code is easier because you can see what kind of objects the code is working with Tool support - Static typing enables reliable refactorings, precise code completion, and other IDE features Thanks to Kotlin’s support for type inference, most of the extra verbosity associated with static typing disappears, because you don’t need to declare types explicitly If you look at the specifics of Kotlin’s type system, you’ll find many familiar concepts Classes, interfaces, and generics work in a way very similar to Java, so most of your Java knowledge should easily transfer to Kotlin Some things are new, though The most important of those is Kotlin’s support for nullable types, which lets you write more reliable programs by detecting possible null pointer exceptions at compile time We’ll come back to nullable types later in this chapter and discuss them in detail in chapter Another new thing in Kotlin’s type system is its support for functional types To see what this is about, let’s look at the main ideas of functional programming and see how it’s supported in Kotlin 1.2.3 Functional and object-oriented As a Java developer, you’re no doubt familiar with the core concepts of object-oriented programming, but functional programming may be new to you The key concepts of functional programming are as follows: First-class functions - You work with functions (pieces of behavior) as values You can store them in variables, pass them as parameters, or return them from other functions Immutability - You work with immutable objects, which guarantees that their state can’t change after their creation No side effects - You use pure functions that return the same result given the same inputs and don’t modify the state of other objects or interact with the outside world What benefits can you gain from writing the code in the functional style?

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