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

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