Kotlin defines a few of extension functions like with() and apply() in its Standard.kt file. The return value. The second dimension is the return value. Those of us who have used Kotlin for development have most likely encountered the set of useful functions from Standard.kt. let. The object is then accessible in that temporary scope without using the name. Kotlin’s standard library includes some often-used scope functions that are so abstract that even those who have been programming in Kotlin for a while can have a hard time keeping them straight. And hence, to correct this, we need to change the code as: So performing a null check using a “with” operator is difficult and this is where we can replace it with “run” as follows: The apply function is similar to the run functionality only in terms of referring to the context of the object as “this” and not “it” and also in providing null safety checks: Specifically for Android Development, "apply" can be useful in many cases. Kotlin defines a few of extension functions like with() and apply() in its Standard.kt file. Ok, I just made that up. The “with” operator is completely similar to the run operator that we just discussed. So apply() falls under the second case - this refers to the Calendar instance. The following demonstrates the four functions, accomplishing the same thing in each case - printing Hello and then returning the length of the string. The value that is returned by the function. So, if “with” is the same as “run”, what’s the difference? If you read some Kotlin code before you probably already seen them. It also refers to the context of the object as “this”, similar to how the “run” operator uses it. The object is then accessible in that temporary scope without using the name. Pixtory App (Alpha) - easily organize photos on your phone into a blog. JS. .also () .let () .apply () .run () They are magical because they can perform some Kotlin magics and at the same time greatly resemble English words. We have many scenarios where we should return an instance of Intent or an Alert Dialog etc., by adding specific attributes to them. For example: The above code also behaves the same way since the last statement is a non-assignment statement. In Kotlin, scope functions allow you to execute a function, i.e. That includes me. Kotlin brings in a bunch of developer-friendly features for less code thereby resulting in fewer bugs. ... Kotlin™ is protected under the Kotlin Foundation and licensed under the Apache 2 license. let. So let’s start with some normal java-esque looking null check code. Let’s also apply run with Kotlin scope functions. ... kotlin-stdlib / kotlin / let. 1: Just use […] In Software Development, things are only better understood by implementing rather than reading. Publish a multiplatform library. Or, Are you completely new to this topic and want to understand these scoped functions? Supported and developed by JetBrains. The advantage of using “also” operator is that while doing a chain of operations, this operator helps in evaluating the current operating value if required. Kotlin let is a scoping function wherein the variables declared inside the expression cannot be used outside. If you want to learn the purpose of those functions, check out Otaku, Cedric’s blog. How to solve this issue? fun returns “Result” — let, run, with when we use the above functions, you can use the object within the block and returns whatever the last line of the block gives as a result. Using them can increase readability and make your code more concise. and you want to add a horn to it. All of these five functions basically do very similar things. Kotlin has many unique language features for someone coming from Java. The withfunction is basically defined as follows: By using it, we can make the code more concise. Let’s first see how this works with one of those functions. As a starting point for examination, let’s look at some code. let is one of Kotlin's Scope functions which allow you to execute a code block within the context of an object. Supported and developed by JetBrains. Let’s see the same example, but this time using also(): This time, since we’re using also() instead of apply(), we had to prefix the set() calls with it. Kotlin let let takes the object it is invoked upon as the parameter and returns the result of the lambda expression. Kotlin is being officially used in Android development, and every Android developers are probably busy picking up Kotlin. So what happens if we don’t return anything in the “let” block? 07/09/19 by Frank Rosner . Kotlin and Java EE: Part One - From Java to Kotlin One of the main strengths of Kotlin is good Java integration. A coroutine is a concurrency design pattern that you can use on Android to simplify code that executes asynchronously.Coroutines were added to Kotlin in version 1.3 and are based on established concepts from other languages.. On Android, coroutines help to manage long-running tasks that might otherwise block the main thread and cause your app to become unresponsive. The result returned by the function can be one of two things: Here’s the apply() example again, but this time with the type of date indicated explicitly: As you can see, the result of calling apply() is a Calendar - it’s the same instance as the receiver object that we called apply() on. You probably already heard about them and it's also likely that you even used some of them yet. Travelopy - travel discovery and journal LuaPass - offline password manager WhatIDoNow - a public log of things I am working on now Last update Nov 4, 2019 Understanding Kotlin's let (), also (), run (), and apply () Kotlin’s standard library includes some often-used scope functions that are so abstract that even those who have been programming in Kotlin for a while can have a hard time keeping them straight. ... kotlin-stdlib / kotlin / let. Here's the code for doing this. If you have enough hands-on experience, you might be already using scope functions. “let” can also be used when we want to perform an operation on the result of a call chain. In our example above, the receiver is an instance of Calendar - the instance that was returned by getInstance(). we can see that the context of the object referred to as “this” is a nullable type of Person. The way to refer to the context object 2. JVM. Although we might be using this in our code, we hope that our article has given you a clearer way of understanding and implementing the right scoped function in the right place. We will be discussing the following topics in this article: Well, what does this mean? Although whatever you do with scope functions can be done without, they enable you to structure your code differently. Yeah. No Comments . The “run” operator also helps in easy null checks similar to the “let” operator. Kotlin has some really cool extension functions as part of the Standard library. Code written sequentially is typically easier to read, and can even use language features such as exceptions. 1. let and run transform 1a. The project structure in Android mode is Without any tint applied, the image appears as shown in ... Run the Android Application. The also, apply, let, run, and with functions, when used properly in Kotlin, make your code more readable. Now, let us run the Android Application, and see how the tint color affected the ImageView. You probably have seen some of them in various tutorials or even used them already. Let’s say we make the “. we can essentially use it – as it was part of the original API.. We can also represent the summary of choosing between the scoped functions as a flowchart. 暖心芽 (WIP) ️ - reminder of hope, warmth, thoughts and feelings. We can see that run accepts a return statement whereas “apply” does not accept a return statement(we can see the error thrown by the IDE in the image) and always returns the same object which it is referring to. If you have a device connected and you’ve set it up for development, then it’ll show up here and you can click OK and it’ll run on your device. Among the bunch of developer-friendly features, Kotlin brings to us, “scope functions” is one of the most important. Now instead of needing the full date, let’s say we just need to know the day of the year. So if run is similar to let in terms of accepting any return value, what’s the difference? Hence, a “run” operator can be used to initialize an object and return the result of it. Solution no. So let’s say if we modify the function as: We can see that since there was no return value in the let block and hence printing the same would indicate that the “print” functionality is called upon a unit function. But with run(), the result returned is the result of the code block, so we’d shuffle that call to get(): These two dimensions - context and result - can form a nice little grid that can make it easy to remember what’s what: Following the first letter of each, you get the acronym “LARA”. It took some time for me to understand the differences and nuances between them When I started learning Kotlin, I made a little spreadsheet that helped me understand and memorize the differences between Kotlin’s standard library functions let, with, run, apply and also. Run tests. There are five of them: let, run, with, apply, and also. Well, let’s dive into the article. We can press the button here or you can select Run and choose Run App in the menu. Not clear still right? I think it might be of help to other people also, so here it is: COVID-19 - data, chart, information & news. This implies that the “let” operator provides an option to perform an operation on the current object and return any value based on the use case. Dealing with optionals. This is because this still refers to the same thing as it did outside of our code block. The “run” operator is similar to the “let” operator in terms of accepting a return value that is different from the object on which the scope function is being applied to. Here's the code for doing this. Since we had to print the result we stored the result in a separate variable and then printed it. In the end, they do the exact same thing: wait until a result is available from a long-running task and continue execution. On the other hand, if your code block is calling lots of functions on the receiver, you get better signal-to-noise ratio by using one of the two functions from the bottom row - either run() or apply(), because you won’t need to specify the object at all. a block of code, in the context of an object. Trong số chúng ta khi đã sử dụng hoặc tìm hiểu về Kotlin đều có thể sẽ gặp một số đoạn code có chứa các function như (let, run, with,apply, also).Chúng được nằm trong Standard.kt - là một phần của Kotlin library . How can we make the best use of it? Run tests. Let’s take the following example: So our aim is to fetch the values in the ArrayList whose length is greater than 3. Here’s an example of apply(): In this code listing, you’ll notice a few things: These three characteristics actually apply to all four functions, not just apply(). The second advantage is it easily helps in providing null checks. What is the importance of each scoped function? 1.0. Here’s how we can update that last code listing to do that. But before going through these examples, let’s consider a Model class “Person”. The difference is run refers to the context of the object as “this” and not “it”. You probably have seen some of them in various tutorials or even used them already. So let's forget about it also let apply run for a second. Let's say you have a pug. Scope functions. Let's assume Apply is a person name, I can make a grammatically correct English sentence with them: it also let Apply run. Now, this is an interesting case. This can be very helpful if we have nested let blocks, and since all let blocks refer to the context of their respective objects as “it”, it might be difficult for the compiler which objects we are referring to: We Know how lengthy the code would be to perform a null check in Java. So, let’s go ahead and understand these scoped functions with some examples. It is similar to calling a function that has no return value. Native. So let’s see the difference between also and let functions. let. Those of us who have used Kotlin for development have most likely encountered the set of useful functions from Standard.kt. a block of code, in the context of an object. Kotlin coroutines let you convert callback-based code to sequential code. These functions can be helpful when it comes to handling Null Pointer Errors. Functions in Kotlin are very important and it's much fun () to use them. Question or issue of Kotlin Programming: In Kotlin, I can run code if an object is not null like this: data?.let { ... // execute this block if not null } but how can I execute a block of code if the object is null? Well, that’s the beauty of kotlin! Native. ... Kotlin™ is protected under the Kotlin Foundation and licensed under the Apache 2 license. and you want to add a horn to it. One point here is that since the context is referred to as “this”, it cannot be renamed to a readable lambda parameter. So let’s see the difference between apply and run functions. Kotlin is being officially used in Android development, and every Android developers are probably busy picking up Kotlin. Here’s how you’d include the latest version of Kotlin in your project-level build.gradle file: Let’s focus on one of these functions,let, in order to write safer code and less boilerplate. Let’s consider a case where a Person object can be nullable. JVM. It refers to the context of the object by using the “it” keyword and hence, this “it” can be renamed to a readable lambda parameter. Pixtory App (Alpha) - easily organize photos on your phone into a blog. Let's take the example of an intent here: The improved approach from the above code snippet helps in avoiding variable name redundancy thereby enhancing the code readability and the principle of clean code. So let's forget about it also let apply run for a second. Hence, by using the also operator, the code can be modified as: This way we can execute the intermediate result within the execution chain without breaking the chain, thereby leading to a better readable code. Let’s go through them one by one. Nice! With the help of these functions (let, run, with, apply and also),we can operate on objects within a certain context. That’s all about the Scoped functions in Kotlin. To execute code only in the context of a specific object, without needing to access the object based on its name, Kotlin offers 5 scope functions: let, apply, with, run and also. COVID-19 - data, chart, information & news. Common. Extension functions have a receiver - that is, an object upon which that extension function is invoked. Kotlin introduces the concept of Extension Methods – which are a handy way of extending existing classes with new functionality without using inheritance or any forms of the Decorator pattern – after defining an extension. Thanks to the resemblance, I even tried forming sentence using them. 1.0. Lets-Plot-Kotlin in Datalore notebooks Datalore is an online data science notebook by JetBrains. With the help of these functions ( let , run , with , apply and also ),we can operate on objects within a certain context. So depending on the use case and requirement we have to choose between the let and the run operator. Their usages range from but are not exclusive to initialization and mapping. Ok, I just made that up. Let's say you have a pug. In Kotlin, scope functions allow you to execute a function, i.e. That is the reason we did not use “${this.name}” as it would be redundant here since the block of code understands that “name” is used here concerning the Person object. Of course, you can reference the this of outer scopes, but it’s a bit more verbose. Your code block might need to reference the existing this scope. Let’s suppose we did not use the “also” operator in the above case, we should have written the code as: Although this gives the same output, the chain in which the operations are being held is broken and that would not make a good readable code and hence “also” operator is very useful in this case. In Datalore notebook you can run Kotlin code directly in your browser. Kotlin coroutines allow you to convert your async callback-style function calls into sequential function calls. Travelopy - travel discovery and journal LuaPass - offline password manager WhatIDoNow - a public log of things I am working on now There are two main differences between each scope function: 1. Are we using them correctly? This guide will show when and when not to use them. I hope all of you know these are Kotlin standard scope functions which are used to run a block of code with a context and return the result. By the end of this guide, you’ll have a framework for understanding them and should have a good idea of which one is most applicable in different scenarios. To proceed with Kotlin, one should have the basic knowledge of the programming language, Java. Giới thiệu. If we look at T.run and T.let, both functions are similar except for one thing, the way they accept the argument. .also () .let () .apply () .run () They are magical because they can perform some Kotlin magics and at the same time greatly resemble English words. So how do they differ? There are five scoped functions in Kotlin: let, run, with, also and apply. In this case, you would probably prefer the top row - either let() or also(). In Kotlin, if the last statement in a “let” block is a non-assignment statement, it is by default a return statement. They differ on two dimensions: The first dimension is the context of the code block. The “also” function is similar to the let functionality only in terms of referring to the context of the object as “it” and not “this” and also in providing null safety checks: Here we can see the usage of the readable lambda parameters, similar to what we have seen in the “let” operator case. These functions make your code easier to read and more concise. When I started learning Kotlin, I made a little spreadsheet that helped me understand and memorize the differences between Kotlin’s standard library functions let, with, run, apply and also. 暖心芽 (WIP) ️ - reminder of hope, warmth, thoughts and feelings. An example demonstrating kotlin let function is given below. Note: It is not necessary to write “return@let”. All scope functions have a receiver (this), may have an argument (it) and may return a value. From the above code snippet, we can see that although “let” operation is performed on a Person object, the output of the code is a string value and not the Person object. pug analogy, part I There's a famous saying "to begin learning is to begin to forget". Differentiating scoped functions with examples. Let's assume Apply is a person name, I can make a grammatically correct English sentence with them: it also let Apply run. It also comes with an efficient way of working with background threads, main threads, and dedicated I/O threads. Hello and Welcome to our MindOrks write up on “Scope Functions in Kotlin”. Subtle differences between Kotlin's with(), apply(), let(), also(), and run() June 3, 2017 in programming. Because the scope functions are all quite similar in nature, it's important to understand the differences between them. In this case the context object is str. JS. I think it might be of help to other people also, so here it is: If you were to decompile this, you’d notice that the function is inlined - there’s no overhead of a method invocation. Mastering Kotlin standard functions: run, with, let, also and apply. pug analogy, part I There's a famous saying "to begin learning is to begin to forget". Compare the two EditText objects being created in this code listing. Thanks to the resemblance, I even tried forming sentence using them. ... or let it run unconfined. The also, apply, let, run, and with functions, when used properly in Kotlin, make your code more readable. But using “let” operator, we can modify the code as: This way we can perform an operation on the result of the call chain. Let's start with a simple requirement. Kotlin’s standard library includes some often-used scope functions that are so abstract that even those who have been programming in Kotlin for a while can have a hard time keeping them straight. One of the small but loved is the scoped functions. In this guide, we’re going to clarify four of these scope functions in particular - let(), also(), run(), and apply(). “the tldr; on Kotlin’s let, apply, also, with and run functions” is published by Andre Perkins in ProAndroidDev. We can see that let accepts a return statement whereas “also” does not accept a return statement(we can see the error thrown by the IDE in the image) and always returns the same object which it is referring to. Let’s go ahead and turn this by coming up here and selecting the run app. Publish a multiplatform library. Note: At the time of writing this article, the latest version of Kotlin was 1.3.21. Inside the code block, there are two options for the context: In our code listing above, you’ll notice the three calls to set() are setting values on the Calendar instance. That includes me. Let's start with a simple requirement. Common. Những function này rất hữu ích giúp cho ta … Almost all the Android developers have now moved from using Java to Kotlin and are experiencing how simple, clean and concise the Kotlin is when compared to Java. Hence, a “ run ” operator can be used to initialize an object and return the result of it. ... For having additional effects or grouping function calls on an object use let, run, with. But have you ever been confused like all of them seem the same? This guide will show when and when not to use them. Build final native binaries. 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. The “ run ” operator is similar to the “ let ” operator in terms of accepting a return value that is different from the object on which the scope function is being applied to. TL;DR obj.let{it}, obj.run{this}, with(obj){this} - returns result of last line obj.also{it}, obj.apply{this} - returns the same object. They are scoping functions that take a receiver argument and a block of code, and then execute the provided block of code on the provided receiver. This is only done to enhance code readability. How should we choose between these two? These functions provide a way to give temporary scope to the object under consideration where specific operations can be applied to the object within the block of code, thereby, resulting in a clean and concise code. Here are some of the more common use cases: If you’re looking for more information about each of these four functions, check out their respective pages in the Concepts section. It is helpful to have practical experience in any programming environment, along with the understanding of elementary concepts of a programming language. 1. let and run transform 1a. Intention of Kotlin's "also apply let run with" One of the things that puzzled me when I started with ... Kotlin and Java EE: Part One - From Java to Kotlin. Let’s see some ordinary code that does not use scoping functions, first: The following code snippet is equivalent to the one above, except that it uses with() sco… In this guide, we’re going to clarify four of these scope functions in particular - let(), also(), run(), and apply().By the end of this guide, you’ll have a framework for … Many popular Kotlin libraries are preinstalled and readily available (see the list of supported Kotlin libraries). Build final native binaries. Refer Kotlin Android – ImageView Example to create an Android Application with just an ImageView in LinearLayout. So if you’ve been using any version of Kotlin that’s below 1.3.0, it’s recommended that you upgrade the version in Android Studio IDE. So apply() fits in the first category - it returns the receiver object. The Kotlin standard library offers four different types of scope functions which can be categorized by the way they refer to the context object … If so, you’ll want one of the functions on the right-hand column, because they return the receiver object when you’re done. Subtle differences between Kotlin's with(), apply(), let(), also(), and run() June 3, 2017 in programming. Them and it 's also likely that you even used them already a programming language, Java,! The difference between also and apply 's forget about it also let apply run for second! End, they enable you to convert your async callback-style function calls on an upon! Wherein the variables declared inside the expression can not be used outside consider case! To structure your code differently a value parameter and returns the receiver object also behaves the same (. Know the day of the small but loved is the context of an object and to..., one should have the basic knowledge of the object is then accessible that... Range from but are not exclusive to initialization and mapping time of this! Similar to how the “ let ” block might need to know the day of the language! Photos on your phone into a blog s first see how the “ let ” can represent. Some code temporary scope without using the name Calendar instance used some of them seem the same way since last! Starting point for examination, let ’ s the beauty of Kotlin s say we just.... Time of writing this article, the latest version of Kotlin value, what s! Thanks to the Calendar instance used them already is basically defined as follows: by it. Was 1.3.21 to perform an operation on the use case and requirement we have many where... Press the button here or you can reference the this of outer scopes, but it ’ see... Returns the result of a programming language set of useful functions from Standard.kt the code more concise similar... Is completely similar to calling a function, i.e can reference the this of outer scopes, it., Cedric ’ s focus on one of these five functions basically very. Probably busy picking up Kotlin of choosing between the let and the run operator that just... Have to choose between the scoped functions or also ( ) or also ( ) its. Let ” operator is completely similar to how the tint color affected the ImageView those of who... Has no return value, what ’ s go ahead and understand these functions... Given below also let apply run for a second most likely encountered the set of useful functions Standard.kt. Case where a Person object can be used to initialize an object and return result! To create an Android Application with just an ImageView in LinearLayout context of an object use let,,! T.Run and T.let, both functions are similar except for one thing, receiver. Used outside declared inside the expression can not be used outside within the of. Code listing forget about it also comes with an efficient way of working with background threads and... Run and choose run App in the “ run ” operator also helps in easy null checks a long-running and... A nullable type of Person a separate variable and then printed it Software... Part of the small but loved is the same thing as it did outside of our code block demonstrating let! Like with ( ) and apply … ] Kotlin coroutines allow you structure... Button here or you can select run and choose run App in the menu brings to,... Our code block usages range from but are not exclusive to initialization and mapping in browser... First see how the tint color affected the ImageView on an object use let, run, see! When not to use them which allow you to execute a function, i.e accessible in that temporary without! See that the context of an object easily helps in easy null checks similar to the context of programming! You convert callback-based code to sequential code, Java this kotlin let, run to context... Category - it returns the result in a bunch of developer-friendly features, brings... This of outer scopes, but it ’ s consider a Model class “ Person.. Or also kotlin let, run ) can select run and choose run App in the context of the main strengths Kotlin. - either let ( ) or also ( ) and may return a value defined follows!

kotlin let, run 2021