So, here comes the role of the reified keyword in Kotlin. To do this, you use flatMap() instead of map(). If I have to write this in programming then I would do it like this – Output: Since the condition returned false, the statement inside “if” was skipped and the statement inside “else” was executed. First of all, when has a better design. How about we take the let function inside some real world class and see how it interacts with the rest of our code. This is why if we want our actual value inside of the let block, we need to safely unwrap the optional type in order to see the actual type and value wrapped inside it. So in the above we have a class to scope some functions to. 12, Jun 19. To add this logic to your code, use special Kotlin keywords such as if and else and when. You can verify that you have all the required variables, then work with them in a safe manner, avoiding broken states and failing fast if data is missing. to safely unwrap our value if it exists is all we’re missing. But the following code does not work, and I have to add run at the beginning of the second {} . This is what let does. Well in Kotlin we can bind to a value if it exists, and we can perform an action if it’s not present too. These functions are all really similar to let however you’ll find the blocks scope of this, the argument it and the result will all be slightly different. Let's look at some examples. let { print ( "Name: ${it}" ) } これは引数を安全にunwrapしたいときにべんり。 Nested if expression. The else branch branch is required if … Kotlin constructor. All we’ve done is add more lines of code. Kotlin™ is protected under the Kotlin Foundation and licensed under the Apache 2 license. if-else ladder. Use an if statement to set up a condition that is met. There are various types of if-else expression in Kotlin: Simple if-else expression. Since let takes a {} block, it feels to me it would be natural that the else (? When a condition is true, it executes the corresponding if expression. Supported and developed by JetBrains. Building complex screens in a RecyclerView with Epoxy. Well in Kotlin we can bind to a value if it exists, and we can perform an action if it’s not present too. One of them is safe call ?. How about we use another extension function to provide an else like clause? kotlinだと次のように書ける val name : String ? Here we go no error! : return // can be simplified to just `property ? Kotlin let let takes the object it is invoked upon as the parameter and returns the result of the lambda expression. Ok so let’s process this information and see what more we could do. These functions can be helpful when it comes to handling Null Pointer Errors. Let’s explore it with a puzzle. If you want to learn the purpose of those functions, check out Otaku, Cedric’s blog. Why can't the else part of `let` take a `{}` block? Python Basics Video Course now on Youtube! Those of us who have used Kotlin for development have most likely encountered the set of useful functions from Standard.kt. Kotlin If-Else If-Else Ladder Expressions We can use the if-else..if-else ladder expression for checking multiple conditions. b. So we’ve started by calling let on our property however we’ve caught ourselves yet another error, what on earth? Here is the code again for the test function, except you can replace xxx with almost* any function from the table. If..Else expression is used when we need to perform some action if a condition is true and we need to perform a different action when a condition is false. inline fun T.let(block: (T) -> R): R, // can be simplified to just `property ? Compose (UI) beyond the UI (Part I): big changes, Greatest Android modularization mistake and how to undo it, Abstract & Test Rendering Logic of State in Android, The Quick Developers Guide to Migrate Their Apps to Android 11. Kotlin knows that a Boolean value can only ever be true or false. Can you trust time measurements in Profiler? Using the safe call operator ?. This means that Kotlin’s equivalent for flatMap() and map()are similar. : return` too which is, Learning Android Development in 2018 [Beginner’s Edition], Google just terminated our start-up Google Play Publisher Account on Christmas day, A Beginner’s Guide to Setting up OpenCV Android Library on Android Studio, Android Networking in 2019 — Retrofit with Kotlin’s Coroutines, REST API on Android Made Simple or: How I Learned to Stop Worrying and Love the RxJava, Android Tools Attributes — Hidden Gems of Android Studio, If the value is an optional, you probably want to unwrap it first with, You can return a value that’s of a different type. In order to use the reified type, we need to use the inline function. : return` too which is // much simpler, but if you want to log anything additional the // let syntax is super flexible. Let's learn about it. Be sure to send me some claps if you enjoyed the read or learned something. You can barely tell what language you’re writting in, how cool is that! The scope of our receiving block is this@MyClass which means we can call our class functions such as fancyPrint when needed, or any other member variables of the class. else myCoolImage = resizeBitmap(myCoolImage,400,600) Simple code to check if photo is horizontal or vertical and to resize it accordingly to that. Something I really missed from Swift, was the guard statement. How it works, is that you bind an optional value to a new locally scoped immutable variable, then you can use it within that scope. fancyPrint(value)} 07, May 19. So how do we handle this? This looks fine for the most part, but we get an error: Since we’re using a mutable variable here, our value could technically be changed by another thread. Kotlin Environment setup with Intellij IDEA. = "John Doe" name ?. Easy fix isn’t it, we know the value isn’t null so lets just force unwrap it with the !! The above if . Though switch performs well only for a larger group of options, Kotlin still converts the when to a switch for expressions more than two options. :) part also takes another {} block. : to guarantee we run one of the conditional branches. Those of us who have used Kotlin for development have most likely encountered the set of useful functions from Standard.kt. Kotlin `let` `else`. Syntax of if-else expression val returnValue = if (condation) { We can use this same strategy to fill in a default value to solve our error from the above section: Pretty cool right! As you’ve seen, let is really quite powerful, and there was a bit more to the function than at first sight. The Puzzle. . let is a pretty useful function from the Kotlin standard library defined as follows: fun T.let(f: (T) -> R): R = f(this) You can refer to a previous article I wrote if you want to understand how this function works, but in this post, I’d like to take a look at the pros and cons of using let . If you understand the grammar of if, then you would understand that there is a subtle problem that could confuse Java developers. The constant case scenario. The systems type inference can determine that the return value will always be non-optional, because we can’t access the rest of the scope if the value isn’t present. The challenge of using these functions is that they are really similar to each other and even experienced users need some time to figure out which function they need. In this tutorial, we’ll be covering an important aspect of programming, namely Kotlin Control Flow statements. We check if a value is not null, and when the value exists we can use it right? Brilliant. Okay not so fast, I don’t think that really covers the function, let’s have a look at its definition: Yea that’s a bit more complicated than I thought initially too. We will understand when to use the inline, when to use noinline and when to use the crossinline in Kotlin depending on our use-case. In this case, Nothing is used to declare that the expression failed to compute a value.Nothing is the type that inherits from all user-defined and built-in types in Kotlin.. Watch Now. Okay no let’s not do that, because the issue is our value could be changed or even set to null which means we’d crash and get a… you guessed it NPE. Kotlin Variables. But lastly you can also return a value from inside the block. . Supported and developed by JetBrains. We require a locally scoped copy of our value to read like so: Finally our code compiles, but I thought Kotlin was suppose to help reduce boilerplate. Effectively this is an early return if a value isn’t present. but before figuring out the difference among both, let’s understand what they are in detail first. In this example we are using let, when using this function we are interested in three things: This is a quite long explanation, instead we can just write it to a table: We can do the same for the rest of the functions. Kotlin if-else Expression As if is an expression it is not used as standalone, it is used with if-else expression and the result of an if-else expression is assign into a variable. Can … Reified keyword in Kotlin. If property exists, then we can capture and use its value, if the value is null we can ensure we show an error. We’ll look into the if else, range, for, while, when repeat, continue break keywords that form the core of any programming language code.. Let’s get started with each of these operators by creating a Kotlin project in our IntelliJ Idea. With Kotlin’s null system, the value is either present, or null, so there’s nothing to unwrap. Kotlin program of using let – ... Kotlin if-else expression. One special collection of relevant functions can be described as "scope functions" and they are part of the Kotlin standard library: let, run, also, apply and with. When mapping an Optional in Java, sometimes you have to unwrap another Optional. In this article, you will learn about when construct in Kotlin with the help of various examples. There are different forms for If-Else statement in Kotlin. Kotlin if-else expression as ternary operator – In Kotlin, if-else can be used as an expression because it returns a value. The following tokens are always interpreted as keywords and cannot be used as identifiers: 1. as 1.1. is used for type casts 1.2. specifies an alias for an import 2. as? In every other condition, it’s an if-else under the hood. Since this is just a plain closure argument, it means we can name the captured property instead of writing it. Fantastic now you know everything there is to know about let! Most of the time, we do mistake while using these keywords inline, noinline, and crossinline in Kotlin. In the above example, we used when as an expression. Syntax to use kotlin if else block as an expression is – Unlike java, there is no ternary operator in Kotlin because if-else return the value according to the condition and works exactly similar to ternary. Unlike Java or any other programming language, you can also use If else block as an expression in kotlin. There’s a brilliant write-up on how these other functions differ below: Thanks for making it this far, I hope you’ll leave with some cool new ideas to explore on your daily coding journey. However it also has a few friends! In the below code if the property exists, It will print it using our fancyPrint method, and then return the string success into a new local property value. Here is a pictorial representation of how an if statement works if used without an else block: Let's take a code example to see the simple if expression in action: With the help of these functions (let, run, with, apply and also),we can operate on objects within a certain context. 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This information and see how it interacts with the! true or false, else branch is.! If ladder been converted this way functions from Standard.kt me some claps if you want learn... Of the article detail first what they are in detail first when it to. Mycoolimage = resizeBitmap ( myCoolImage,400,600 ) Simple code to understand how and why it has been converted this way why! Compact alternative to Java copy of the conditional expression is – kotlinだと次のように書ける val name: $ { it } )... Can not be used here comes the role of the reified keyword in Kotlin had no Errors, ’!