The Kotlin standard library offers four different types of scope functions which can be categorized by the way they refer to the context object … 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. Among the bunch of developer-friendly features, Kotlin brings to us, “scope functions” is one of the most important. Subtle differences between Kotlin's with(), apply(), let(), also(), and run() June 3, 2017 in programming. Supported and developed by JetBrains. This guide will show when and when not to use them. .also () .let () .apply () .run () They are magical because they can perform some Kotlin magics and at the same time greatly resemble English words. So apply() fits in the first category - it returns the receiver object. In Kotlin, scope functions allow you to execute a function, i.e. 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. 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. So, let’s go ahead and understand these scoped functions with some examples. So depending on the use case and requirement we have to choose between the let and the run operator. pug analogy, part I There's a famous saying "to begin learning is to begin to forget". It took some time for me to understand the differences and nuances between them Those of us who have used Kotlin for development have most likely encountered the set of useful functions from Standard.kt. 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 . It also refers to the context of the object as “this”, similar to how the “run” operator uses it. Here’s how you’d include the latest version of Kotlin in your project-level build.gradle file: Kotlin is being officially used in Android development, and every Android developers are probably busy picking up Kotlin. 1. let and run transform 1a. Your code block might need to reference the existing this scope. 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. 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. Here's the code for doing this. Ok, I just made that up. Now, let us run the Android Application, and see how the tint color affected the ImageView. Now instead of needing the full date, let’s say we just need to know the day of the year. pug analogy, part I There's a famous saying "to begin learning is to begin to forget". Publish a multiplatform library. This guide will show when and when not to use them. That includes me. Pixtory App (Alpha) - easily organize photos on your phone into a blog. Travelopy - travel discovery and journal LuaPass - offline password manager WhatIDoNow - a public log of things I am working on now With the help of these functions (let, run, with, apply and also),we can operate on objects within a certain context. 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. Kotlin and Java EE: Part One - From Java to Kotlin One of the main strengths of Kotlin is good Java integration. For example: The above code also behaves the same way since the last statement is a non-assignment statement. Well, that’s the beauty of kotlin! All scope functions have a receiver (this), may have an argument (it) and may return a value. Of course, you can reference the this of outer scopes, but it’s a bit more verbose. The second dimension is the return value. Hence, a “run” operator can be used to initialize an object and return the result of it. Travelopy - travel discovery and journal LuaPass - offline password manager WhatIDoNow - a public log of things I am working on now I think it might be of help to other people also, so here it is: We can press the button here or you can select Run and choose Run App in the menu. Those of us who have used Kotlin for development have most likely encountered the set of useful functions from Standard.kt. let. ... Kotlin™ is protected under the Kotlin Foundation and licensed under the Apache 2 license. 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. We can also represent the summary of choosing between the scoped functions as a flowchart. Kotlin let is a scoping function wherein the variables declared inside the expression cannot be used outside. That includes me. ... For having additional effects or grouping function calls on an object use let, run, with. No Comments . How can we make the best use of it? If you read some Kotlin code before you probably already seen them. “the tldr; on Kotlin’s let, apply, also, with and run functions” is published by Andre Perkins in ProAndroidDev. Let’s focus on one of these functions,let, in order to write safer code and less boilerplate. Differentiating scoped functions with examples. Using them can increase readability and make your code more concise. Since we had to print the result we stored the result in a separate variable and then printed it. In this case, you would probably prefer the top row - either let() or also(). Run tests. Or, Are you completely new to this topic and want to understand these scoped functions? 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”. 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. One of the small but loved is the scoped functions. So apply() falls under the second case - this refers to the Calendar instance. we can essentially use it – as it was part of the original API.. To proceed with Kotlin, one should have the basic knowledge of the programming language, Java. 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. ... kotlin-stdlib / kotlin / let. 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. Let's start with a simple requirement. The following demonstrates the four functions, accomplishing the same thing in each case - printing Hello and then returning the length of the string. In Datalore notebook you can run Kotlin code directly in your browser. If so, you’ll want one of the functions on the right-hand column, because they return the receiver object when you’re done. Let’s go through them one by one. Ok, I just made that up. let is one of Kotlin's Scope functions which allow you to execute a code block within the context of an object. JS. So let's forget about it also let apply run for a second. 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. Let’s go ahead and turn this by coming up here and selecting the run app. With the help of these functions ( let , run , with , apply and also ),we can operate on objects within a certain context. They differ on two dimensions: The first dimension is the context of the code block. Kotlin let let takes the object it is invoked upon as the parameter and returns the result of the lambda expression. Run tests. Hence, a “ run ” operator can be used to initialize an object and return the result of it. JVM. In the end, they do the exact same thing: wait until a result is available from a long-running task and continue execution. 1: Just use […] 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. 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. Kotlin defines a few of extension functions like with() and apply() in its Standard.kt file. Let's start with a simple requirement. 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. In this guide, we’re going to clarify four of these scope functions in particular - let(), also(), run(), and apply(). Extension functions have a receiver - that is, an object upon which that extension function is invoked. So if run is similar to let in terms of accepting any return value, what’s the difference? If we look at T.run and T.let, both functions are similar except for one thing, the way they accept the argument. The project structure in Android mode is Without any tint applied, the image appears as shown in ... Run the Android Application. 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. Kotlin has some really cool extension functions as part of the Standard library. Giới thiệu. In Kotlin, scope functions allow you to execute a function, i.e. JVM. This is because this still refers to the same thing as it did outside of our code block. 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. Native. These functions make your code easier to read and more concise. It is similar to calling a function that has no return value. Functions in Kotlin are very important and it's much fun () to use them. So let’s see the difference between apply and run functions. 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? 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. The object is then accessible in that temporary scope without using the name. Because the scope functions are all quite similar in nature, it's important to understand the differences between them. JS. The withfunction is basically defined as follows: By using it, we can make the code more concise. ... kotlin-stdlib / kotlin / let. 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. The return value. let. Build final native binaries. 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. Publish a multiplatform library. But have you ever been confused like all of them seem the same? Thanks to the resemblance, I even tried forming sentence using them. Here’s how we can update that last code listing to do that. a block of code, in the context of an object. Let's assume Apply is a person name, I can make a grammatically correct English sentence with them: it also let Apply run. How to solve this issue? Let’s take the following example: So our aim is to fetch the values in the ArrayList whose length is greater than 3. 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 … The second advantage is it easily helps in providing null checks. 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