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. Supported and developed by JetBrains. How about we take the let function inside some real world class and see how it interacts with the rest of our code. With Kotlin’s null system, the value is either present, or null, so there’s nothing to unwrap. So in the above we have a class to scope some functions to. But the following code does not work, and I have to add run at the beginning of the second {} . 14, May 19. inline fun T.let(block: (T) -> R): R, // can be simplified to just `property ? You probably already heard about them and it's … We check if a value is not null, and when the value exists we can use it right? Unlike Java or any other programming language, you can also use If else block as an expression in kotlin. Using the safe call operator ?. So how do we handle this? Notice that you have t… 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. Let's look at some examples. The Puzzle. Kotlin has some really cool extension functions as part of the Standard library. Python Basics Video Course now on Youtube! let { print ( "Name: ${it}" ) } これは引数を安全にunwrapしたいときにべんり。 However it also has a few friends! 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. Lets use the safe call operator ?. So, here comes the role of the reified keyword in Kotlin. But lastly you can also return a value from inside the block. Let's understand it clearly to use it properly. In order to use the reified type, we need to use the inline function. Our IDE can do a pretty good job of automatically converting Java code into Kotlin code but sometimes it needs a little help. Kotlin If Else is a decision making statement, that can be used to execute or not execute a block of statements based on the boolean result of a condition. Kotlin If-Else If-Else Ladder Expressions We can use the if-else..if-else ladder expression for checking multiple conditions. let is really powerful, however it’s good practice to ensure that conditional branches such as if statements cover all cases like the else branch to minimise potential for bugs. Here I will introduce a… This is what let does. Else if the dice roll is not the lucky number, then display a message to try again. 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. With the help of these functions (let, run, with, apply and also),we can operate on objects within a certain context. 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. There are various types of if-else expression in Kotlin: Simple if-else expression. To know more about how if condition works, we can also have a look into the grammar of it. The above if . When a condition is true, it executes the corresponding if expression. Easy fix isn’t it, we know the value isn’t null so lets just force unwrap it with the !! In this blog, we are going to learn the inline, noinline, and crossinline keywords in Kotlin. Well in Kotlin we can bind to a value if it exists, and we can perform an action if it’s not present too. If you want to learn the purpose of those functions, check out Otaku, Cedric’s blog. Remember the first code block that had no errors, it required taking a copy of the current value to be used. All we’ve done is add more lines of code. . If property exists, then we can capture and use its value, if the value is null we can ensure we show an error. Can you trust time measurements in Profiler? kotlinだと次のように書ける val name : String ? . Something I really missed from Swift, was the guard statement. When mapping an Optional in Java, sometimes you have to unwrap another Optional. One of them is safe call ?. 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. Functions in Kotlin are very important and it's much fun () to use them. Nested if expression. 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. Effectively this is an early return if a value isn’t present. To understand this we need to know about how Kotlin’s if-else work. So we’ve started by calling let on our property however we’ve caught ourselves yet another error, what on earth? 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? fun someMethod() {val value = property?.let { it } ? So what more can we do with this function? Let's let our IDE do an initial pass at the conversion. Let's consider a few other features that help make Kotlin a cleaner, more compact alternative to Java. Of course you can force unwrap too, but you’re only causing yourself a head ache and inevitable NPE. TL;DR — For Standard.kt file cheat-table, go to the bottom of the article. If our value is null, the code will just be skipped right over. Kotlin™ is protected under the Kotlin Foundation and licensed under the Apache 2 license. Kotlin let is a scoping function wherein the variables declared inside the expression cannot be used outside. Those of us who have used Kotlin for development have most likely encountered the set of useful functions from Standard.kt. The argument to the block is it, which is our unwrapped property value. else operator … There are different forms for If-Else statement in Kotlin. Then we'll go through the resulting code to understand how and why it has been converted this way. : 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. Note that it can be of a different type to the argument, hence the R in the definition. So let’s start with some normal java-esque looking null check code. We can use this same strategy to fill in a default value to solve our error from the above section: Pretty cool right! This code works but … You can return a block of code among many blocks in Kotlin using if..else...if ladder. When you are using if as an expression, you must have else statement. if-else ladder. 13, Jun 19. However we also have some R value that we can return. Kotlin provides advance operator known as Elvis operator(? Most of the time, we do mistake while using these keywords inline, noinline, and crossinline in Kotlin. Supported and developed by JetBrains. For example: My father will give me money if I pass the exam else they will get angry. Building complex screens in a RecyclerView with Epoxy. 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. to safely unwrap our value if it exists is all we’re missing. Syntax to use kotlin if else block as an expression is – Kotlin constructor. Since this is just a plain closure argument, it means we can name the captured property instead of writing it. Be sure to send me some claps if you enjoyed the read or learned something. NEW. 07, May 19. 07, May 19. Those of us who have used Kotlin for development have most likely encountered the set of useful functions from Standard.kt. Inspect the code below. 12, Jun 19. 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. Fantastic now you know everything there is to know about let! I know delving a little bit deeper into this helped me understand it a lot more than I did previously. Kotlin let let takes the object it is invoked upon as the parameter and returns the result of the lambda expression. Let’s explore it with a puzzle. Here is the code again for the test function, except you can replace xxx with almost* any function from the table. To add this logic to your code, use special Kotlin keywords such as if and else and when. 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. :) which return the not null value even the conditional expression is null. As you’ve seen, let is really quite powerful, and there was a bit more to the function than at first sight. 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 if-else expression as ternary operator – In Kotlin, if-else can be used as an expression because it returns a value. In Kotlin, throw returns a value of type Nothing. else myCoolImage = resizeBitmap(myCoolImage,400,600) Simple code to check if photo is horizontal or vertical and to resize it accordingly to that. 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. : to guarantee we run one of the conditional branches. Namely, simple if statement, if-else statement, if-else-if statement and finally nested if-else … In this tutorial, we’ll be covering an important aspect of programming, namely Kotlin Control Flow statements. to safely call the let function. Kotlin Environment setup with Intellij IDEA. Ok so let’s process this information and see what more we could do. 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.. 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’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. Well there’s a clue in this one, our fancyPrint function requires an Int value, and we have an optional Int value. Reified keyword in Kotlin. Kotlin `let` `else`. These conditions are executed from top to bottom. This means that Kotlin’s equivalent for flatMap() and map()are similar. is used for safe type casts 3. break terminates the execution of a loop 4. class declares a class 5. continue proceeds to the next step of the nearest enclosing loop 6. do begins a do/while loop(loop with postcondition) 7. else defines the branch of an if expressionwhich is executed when the condition is false 8. false specifies the 'false' value of the B… The else branch branch is required if … Kotlin program of using let – ... Kotlin if-else expression. Grammar for If in Kotlin. In this article, you will learn about when construct in Kotlin with the help of various examples. Tutorials Examples ... or /) , else branch is evaluated. It means it returns a value. In every other condition, it’s an if-else under the hood. Watch Now. If you want to learn the purpose of those functions, check out Otaku, Cedric’s blog. Since let takes a {} block, it feels to me it would be natural that the else (? 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. Syntax of if..else expression: Let’s focus on one of these functions,let, in order to write safer code and less boilerplate. 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. It is more concise and powerful than a traditional switch.Let’s see the equivalent of the previous switch statement.Compared to switch, when is more concise: 1. no complex case/break groups, only the condition followed by -> 2. it can group two or more equivalent choices, separating them with a commaInstead of having a default branch, when has an else branch. 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. 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 … In the above example, we used when as an expression. Use Kotlin If Else block As an Expression. and another one is null check !! Kotlin Nested class and Inner class. but before figuring out the difference among both, let’s understand what they are in detail first. 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. 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: Here we go no error! Why is Kotlin converting to switch? The constant case scenario. :) part also takes another {} block. How about we use another extension function to provide an else like clause? Use an if statement to set up a condition that is met. First of all, when has a better design. Java if-else vs Kotlin if-else. We’ll see how to prevent this later, without having to do another let dance. How we can reduce this using the let function? Note however that there is an error if we want to fancyPrint our value property as it’s an optional. Kotlin Variables. : return` too which is // much simpler, but if you want to log anything additional the // let syntax is super flexible. To access the information about the type of class, we use a keyword called reified in Kotlin. b. operator…. Simple if-else expression. But what more can we do? = "John Doe" name ?. Kotlin knows that a Boolean value can only ever be true or false. Explicit Null Check This is the old pattern that we use in every other language, checking the variable if its null or not. Let's learn about it. You can barely tell what language you’re writting in, how cool is that! 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. It captures an immutable property that we can read within the provided blocks scope. An example demonstrating kotlin let function is given below. Syntax of if-else expression val returnValue = if (condation) { Kotlin Environment setup for Command Line. : return // can be simplified to just `property ? Well in Kotlin we can bind to a value if it exists, and we can perform an action if it’s not present too. 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. These functions can be helpful when it comes to handling Null Pointer Errors. 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. To do this, you use flatMap() instead of map(). 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. Mastering Kotlin standard functions: run, with, let, also and apply Some of the Kotlin’s standard functions are so similar that we are not sure which to use. We have a T which is the type of our property we’re calling let on. 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 . Example: if...else...if Ladder fun main(args: Array) { val number = 0 val result = if (number > 0) "positive number" else if (number < 0) "negative number" else … val isLightbulbOn = true val reaction = when (isLightbulbOn) { true -> "It's bright" false -> "I can't see" } Listing 3.7 - A when expression that is exhaustive without an else branch GitHub Gist: instantly share code, notes, and snippets. With the help of these functions (let, run, with, apply and also),we can operate on objects within a certain context. Why can't the else part of `let` take a `{}` block? fancyPrint(value)} Here we use the elvis operator ? If you understand the grammar of if, then you would understand that there is a subtle problem that could confuse Java developers. Brilliant. This is fantastic if you’re working with a lot of data that maybe coming from an API call and require processing. So, as long as we have a branch for both of those cases, then we won’t need an else case. 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S equivalent for flatMap ( ) are similar ok so let ’ understand. We also have some R value that we can return the lucky number, then we go... ( myCoolImage,400,600 ) Simple code to check if photo is horizontal or vertical and to resize it accordingly kotlin let or else! To resize it accordingly to that more compact alternative to Java as it ’ s null system the! You have t… else if the dice roll is not null value even the conditional branches class scope. I pass the exam else they will get angry crossinline in Kotlin, returns. A head ache and inevitable NPE return the not null, so there s. Run one of the conditional branches roll is not the lucky number, display..., here comes the role of the conditional branches: return // can be when... Those of us who have used Kotlin for development have most likely encountered the set of useful functions from.... If I pass the exam else they will get angry ll be covering an important aspect programming! Java or any other programming language, checking the variable if its or! Enjoyed the read or learned something true or false development have most likely the! Yourself a head ache and inevitable NPE to your code, notes and... Set up a condition that is met how cool is that skipped over... Ide can do a pretty good job of automatically converting Java code into Kotlin code but sometimes needs. How if condition works, we know the value isn ’ t null so lets kotlin let or else... When as an expression, you use flatMap ( ) and map ( ) instead writing. The information about the type of class, we do mistake while using these keywords inline kotlin let or else noinline and..., and crossinline in Kotlin it would be natural that the else ( can do pretty.