Build final native binaries. Let’s focus on one of these functions,let, in order to write safer code and less boilerplate. Not clear still right? 1.0. 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 coroutines let you convert callback-based code to sequential code. 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. Compare the two EditText objects being created in this code listing. Let's start with a simple requirement. 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. If you have enough hands-on experience, you might be already using scope functions. This is because this still refers to the same thing as it did outside of our code block. In this guide, we’re going to clarify four of these scope functions in particular - let(), also(), run(), and apply(). 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. To proceed with Kotlin, one should have the basic knowledge of the programming language, Java. Common. So, let’s go ahead and understand these scoped functions with some examples. let. 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. Run tests. Refer Kotlin Android – ImageView Example to create an Android Application with just an ImageView in LinearLayout. 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. Now, this is an interesting case. Supported and developed by JetBrains. In Kotlin, if the last statement in a “let” block is a non-assignment statement, it is by default a return statement. 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. 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. Supported and developed by JetBrains. That includes me. Pixtory App (Alpha) - easily organize photos on your phone into a blog. Kotlin has some really cool extension functions as part of the Standard library. Those of us who have used Kotlin for development have most likely encountered the set of useful functions from Standard.kt. So let's forget about it also let apply run for a second. 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. COVID-19 - data, chart, information & news. 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. Are we using them correctly? There are two main differences between each scope function: 1. These functions can be helpful when it comes to handling Null Pointer Errors. Kotlin defines a few of extension functions like with() and apply() in its Standard.kt file. 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 … I think it might be of help to other people also, so here it is: So how do they differ? With the help of these functions ( let , run , with , apply and also ),we can operate on objects within a certain context. 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. This is only done to enhance code readability. Solution no. They differ on two dimensions: The first dimension is the context of the code block. Những function này rất hữu ích giúp cho ta … You probably have seen some of them in various tutorials or even used them already. Let's say you have a pug. Here's the code for doing this. Kotlin has many unique language features for someone coming from Java. pug analogy, part I There's a famous saying "to begin learning is to begin to forget". It is helpful to have practical experience in any programming environment, along with the understanding of elementary concepts of a programming language. ... or let it run unconfined. let. 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. How should we choose between these two? In Kotlin, scope functions allow you to execute a function, i.e. We have many scenarios where we should return an instance of Intent or an Alert Dialog etc., by adding specific attributes to them. Let’s take the following example: So our aim is to fetch the values in the ArrayList whose length is greater than 3. Hence, a “ run ” operator can be used to initialize an object and return the result of it. In this case the context object is str. .also () .let () .apply () .run () They are magical because they can perform some Kotlin magics and at the same time greatly resemble English words. In Datalore notebook you can run Kotlin code directly in your browser. 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. These functions make your code easier to read and more concise. Kotlin let let takes the object it is invoked upon as the parameter and returns the result of the lambda expression. Lets-Plot-Kotlin in Datalore notebooks Datalore is an online data science notebook by JetBrains. Travelopy - travel discovery and journal LuaPass - offline password manager WhatIDoNow - a public log of things I am working on now Native. 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. 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? For example: The above code also behaves the same way since the last statement is a non-assignment statement. This guide will show when and when not to use them. This guide will show when and when not to use them. The “with” operator is completely similar to the run operator that we just discussed. Let's assume Apply is a person name, I can make a grammatically correct English sentence with them: it also let Apply run. So what happens if we don’t return anything in the “let” block? 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 consider a case where a Person object can be nullable. Your code block might need to reference the existing this scope. In Software Development, things are only better understood by implementing rather than reading. JVM. We can also represent the summary of choosing between the scoped functions as a flowchart. Let’s also apply run with Kotlin scope functions. So let's forget about it also let apply run for a second. 1. let and run transform 1a. 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 . So let’s see the difference between also and let functions. The return value. If so, you’ll want one of the functions on the right-hand column, because they return the receiver object when you’re done. So apply() falls under the second case - this refers to the Calendar instance. Among the bunch of developer-friendly features, Kotlin brings to us, “scope functions” is one of the most important. Here’s how we can update that last code listing to do that. let. Subtle differences between Kotlin's with(), apply(), let(), also(), and run() June 3, 2017 in programming. But before going through these examples, let’s consider a Model class “Person”. The second advantage is it easily helps in providing null checks. 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. Kotlin and Java EE: Part One - From Java to Kotlin One of the main strengths of Kotlin is good Java integration. Thanks to the resemblance, I even tried forming sentence using them. and you want to add a horn to it. Dealing with optionals. “the tldr; on Kotlin’s let, apply, also, with and run functions” is published by Andre Perkins in ProAndroidDev. All of these five functions basically do very similar things. You probably already heard about them and it's also likely that you even used some of them yet. There are five of them: let, run, with, apply, and also. “let” can also be used when we want to perform an operation on the result of a call chain. 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. 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. Yeah. 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. COVID-19 - data, chart, information & news. Build final native binaries. So, if “with” is the same as “run”, what’s the difference? There are five scoped functions in Kotlin: let, run, with, also and apply. 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”. Or, Are you completely new to this topic and want to understand these scoped functions? Publish a multiplatform library. Code written sequentially is typically easier to read, and can even use language features such as exceptions. We can press the button here or you can select Run and choose Run App in the menu. The also, apply, let, run, and with functions, when used properly in Kotlin, make your code more readable. ... Kotlin™ is protected under the Kotlin Foundation and licensed under the Apache 2 license. Now instead of needing the full date, let’s say we just need to know the day of the year. The object is then accessible in that temporary scope without using the name. How can we make the best use of it? Although whatever you do with scope functions can be done without, they enable you to structure your code differently. Subtle differences between Kotlin's with(), apply(), let(), also(), and run() June 3, 2017 in programming. The Kotlin standard library offers four different types of scope functions which can be categorized by the way they refer to the context object … As a starting point for examination, let’s look at some code. Ok, I just made that up. Here's the code for doing this. Nice! JS. Hence, a “run” operator can be used to initialize an object and return the result of it. If you were to decompile this, you’d notice that the function is inlined - there’s no overhead of a method invocation. 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. We will be discussing the following topics in this article: Well, what does this mean? 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 object is then accessible in that temporary scope without using the name. ... For having additional effects or grouping function calls on an object use let, run, with. Now, let us run the Android Application, and see how the tint color affected the ImageView. Functions in Kotlin are very important and it's much fun () to use them. Many popular Kotlin libraries are preinstalled and readily available (see the list of supported Kotlin libraries). Mastering Kotlin standard functions: run, with, let, also and apply. 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. 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. 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. 1: Just use […] pug analogy, part I There's a famous saying "to begin learning is to begin to forget". So if run is similar to let in terms of accepting any return value, what’s the difference? The value that is returned by the function. Thanks to the resemblance, I even tried forming sentence using them. No Comments . ... Kotlin™ is protected under the Kotlin Foundation and licensed under the Apache 2 license. Let’s say we make the “. It took some time for me to understand the differences and nuances between them Well, let’s dive into the article. 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. 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. 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. One point here is that since the context is referred to as “this”, it cannot be renamed to a readable lambda parameter. Let's say you have a pug. 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… All scope functions have a receiver (this), may have an argument (it) and may return a value. The way to refer to the context object 2. What is the importance of each scoped function? So let’s start with some normal java-esque looking null check code. Well, that’s the beauty of kotlin! In our example above, the receiver is an instance of Calendar - the instance that was returned by getInstance(). The second dimension is the return value. 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. 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. That’s all about the Scoped functions in Kotlin. The following demonstrates the four functions, accomplishing the same thing in each case - printing Hello and then returning the length of the string. 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. It also comes with an efficient way of working with background threads, main threads, and dedicated I/O threads. we can essentially use it – as it was part of the original API.. 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. The also, apply, let, run, and with functions, when used properly in Kotlin, make your code more readable. 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. Let’s first see how this works with one of those functions. Ok, I just made that up. 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. 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. Publish a multiplatform library. we can see that the context of the object referred to as “this” is a nullable type of Person. 1.0. You probably have seen some of them in various tutorials or even used them already. In this case, you would probably prefer the top row - either let() or also(). How to solve this issue? The project structure in Android mode is Without any tint applied, the image appears as shown in ... Run the Android Application. Let's assume Apply is a person name, I can make a grammatically correct English sentence with them: it also let Apply run. Note: At the time of writing this article, the latest version of Kotlin was 1.3.21. It is similar to calling a function that has no return value. Differentiating scoped functions with examples. If you want to learn the purpose of those functions, check out Otaku, Cedric’s blog. Kotlin let is a scoping function wherein the variables declared inside the expression cannot be used outside. Let’s go through them one by one. 07/09/19 by Frank Rosner . Common. With the help of these functions (let, run, with, apply and also),we can operate on objects within a certain context. Travelopy - travel discovery and journal LuaPass - offline password manager WhatIDoNow - a public log of things I am working on now So apply() fits in the first category - it returns the receiver object. That includes me. Extension functions have a receiver - that is, an object upon which that extension function is invoked. Those of us who have used Kotlin for development have most likely encountered the set of useful functions from Standard.kt. Native. let is one of Kotlin's Scope functions which allow you to execute a code block within the context of an object. 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Best use of it Pointer Errors read some Kotlin code directly in your browser mastering standard... And then printed it the Apache 2 license dimensions: the first dimension is the context of the expression. Block within the context of the lambda expression that we just need to the! Kotlin defines a few of extension functions kotlin let, run with ( ) in its Standard.kt file the. To let in terms of accepting any return value, what does this mean it. Many popular Kotlin libraries are preinstalled and readily available ( see the difference between and! Let you convert callback-based code to sequential code part I there 's a famous saying `` begin! What does this mean what happens if we don ’ t return anything in first. Code block might need to know the day of the small but loved is the same brings a! 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