Think of tangible data types, such as Circle, User, Tweet and Article. In swift how to copy a struct with one with only one different field. Why use structs by default? Array of Structs in Swift. Now I want a copy of state but with b = 4. If you want to create a function that can mutate (or change) the properties of a struct, you have to explicitly declare the function with mutating. Give the Swift … Well, that's not strictly true: Swift uses a technique called "copy on write" which means it only actually copies your data if you try to change it. You can think struct has two modes: mutable and immutable.If you assign a struct value to an immutable storage (we call it let or constant in Swift) the value becomes immutable mode, and you cannot change any state in the value. Great! Eaga Trust - Information for Cash - Scam? If you’re looking at a SWIFT message for the first time, it can be a bit daunting. First, try out the example. Confusion about reps vs time under tension: aren't these two things contradictory? Question or problem with Swift language programming: I know that swift will optimize to copy on write for arrays but will it do this for all structs? There may be something you also hear over and over again like: struct is value-semantic, struct is faster. Even though this sounds very expensive, many of the copies can be optimized away by the compiler, and Swift tries hard to make the copies very cheap. Struct Semantics in Swift Implementing Copy-on-Write efficiently . Join Stack Overflow to learn, share knowledge, and build your career. When you copy a class, you end up with two references to one instance of the data. Taking the above code example shows this important difference as … See how the properties ID, productName, productPrice and isPaid have an initial value? To the untrained eye the whole SWIFT message structure can look like gobbledygook. In Swift 5.1, you can use the memberwise initializer in conjunction with default property values, and leave out initializer parameters to set them to their default value. Note, that while you use placeholder values for constants a and b you are not able to construct instance of A with any other values but this placeholders. Thanks for sharing this. That means for example that a delegate or datasource of UITableView must not be a struct but a class because UIKit is still written in Objective-C. In Swift, structs are value types whereas classes are reference types. The syntax does not appear to be a valid Swift construct – Matteo Piombo Feb 16 '15 at 18:08 Thanks for contributing an answer to Stack Overflow! Is it really as it being said or is there anything hidden behind? A Swift property does not have a corresponding instance variable, and the backing store for a property is not accessed directly. If you define a struct in Swift, you can’t expose it to Objective-C source code. Like this: Why is the makePurchase(...) function marked with the mutating keyword? In Swift, classes and structures feel and behave very similarly, but there are a number of key differences that you need to understand to avoid common pitfalls. Undo/Redo with immutable objects. How can I do this without constructing a new object and having to specify a value for every property? Yes! Related. Reinder de Vries is a professional iOS developer. Back in the 90s and early 00s, when Google Docs didn’t exist yet and devices from Apple weren’t as popular, the primary way to create, edit and share documents and spreadsheets was Microsoft Office and its proprietary .doc and .xls binary formats. We’ll also dive into the differences between structs and classes, and when you should use one or the other. It’s a crucial difference, and it … Swift has rich value types, which is a new experience for many software developers. Array of Structs in Swift. Because Cat is a struct, and a struct is a value type, each variable keeps a copy of their own data. You may write custom method that change any value in struct also: If you can live with the properties being mutable, this is an alternative approach. You can also create a Receipt object, keeping the initial values as they are, and changing the properties directly. In other words, being Array-like in Swift is a bottom-up approach where Objective-C takes a top-down approach. A struct is a value type and will create a unique copy for each new reference. This means that if you pass a structure to a function, it will be passed as a copy rather than a reference to the original object. In Swift, you use structs to wrap and store complex data types. Because Cat is a struct, and a struct is a value type, each variable keeps a copy of their own data. We can change these values later on, or use the synthesized default initializer to set the properties when creating a new instance. Swift, Struct & Inheritance: How to balance the will of using Struct & Value Types and the need for Inheritance? How to copy objects in Swift using copy() Swift version: 5.2. I really like @Shadow answer, but I had a hard time adapting it to a scenario were the fields of the struct could be nullable, so I decided to use the builder pattern instead. This has opened the door for the functionalists to ride in. A computed property is, like its name implies, a property that changes its value dynamically based on a computation. Hey, that’s interesting! Imagine we’re building a Twitter app. The DataManager class has a stored property called data, which is initialized with a new, empty array of String values. If I want to represent my view controller's state as a single struct and then implement an undo mechanism, how would I change, say, one property on the struct and, at the same time, get a copy of the the previous state? In our book Advanced Swift, we show how to implement your own copy-on-write structs in detail.This blogpost shows the same technique, but in less detail. In this tutorial, we’ve discussed what structs are and how you can use them. Using let on a struct makes that object a constant. Structs automatically get a so-called memberwise initializer, which is similar to a default initializer, even if you don’t declare default values for the its properties. Write initializer instead. So far so good! Let's find … Comparing a struct with a class – a class will share a copy of the data, and merely copies the reference to that data. Copied to Clipboard. "Should I use struct or class?" I am trying to implement an array of structs in swift to organize a set of data. There are two main complex data types in Swift – objects and structs – and they do so many things similarly that you'd be forgiven for not being sure exactly where they differ. Without any other information, Swift creates an array that includes the specified values, automatically inferring the array’s Element type. In this lesson, we're going to explore the fundamental building blocks of object-oriented programming in Swift, classes and structures. At the end of this tutorial, we’ll discuss how structs and classes are similar – but different. Comparing a struct with a class – a class will share a copy of the data, and merely copies the reference to that data. Let’s move on, to learn more about value types! The struct megwas created as a variable, therefore we can change its variables and rename the dog. I prefer to use the functional approach because it doesn’t have any side-effects, I can keep my variables as constants, and of course, it is super clean to test! 545. rev 2021.1.18.38333, Stack Overflow works best with JavaScript enabled, Where developers & technologists share private knowledge with coworkers, Programming & related technical career opportunities, Recruit tech talent & build your employer brand, Reach developers & technologists worldwide. The best way I have found is to write an initializer method that takes an object of the same type to "copy", and then has optional parameters to set each individual property that you want to change. With big structs i got a stack overflow crash with same way of implementation. I've updated the question to remove the placeholders. We’ve also discussed how structs and classes are similar but different, and how you can make your Swift code better by using the right data type. How can I solve a system of linear equations? Passing a copy of a struct that is 64-bits wide is no more expensive than passing a pointer to that same struct. Copy link Quote reply madnik commented Sep 16, 2015. Swift makes your work safer because it tries to make it obvious when you have a bug by showing you problems at compile time, rather than hanging you out to dry at runtime.The key to making this happen is the Swift type system:Swift types are powerful, despite there being only six of them. Well, one of the key areas is down to copying: two variables can point at the same object so that changing one changes them both, whereas if you tried that with structs you'd find that Swift creates a full copy so that changing the copy … More investigation, seems that at least in Swift version 4.0.3, structs have copy on write enabled by default. If you want to learn more about the differences between structs and classes, check out this tutorial. Swift makes it easy to create arrays in your code using an array literal: simply surround a comma-separated list of values with square brackets. Just like classes, structs can define and use a bunch of Swift’s default building blocks: We’ve already looked at how structs can define properties. Three big selling points of Swift are its safety, speed and simplicity.Safety implies that it’s difficult to accidentally write code that runs amok, corrupting memory and producing hard-to-find bugs. your coworkers to find and share information. The above code is similar to how classes are declared in Swift. Finally, structs can also do a bunch of things that classes can do too: Can classes do things that structs cannot? The idea is that a lot of bugs in programming today are due to having the wrong state. There are two main complex data types in Swift – objects and structs – and they do so many things similarly that you'd be forgiven for not being sure exactly where they differ. Advantage is that it works for every struct and there's no need to change the function upon adding a property: You could also have an extension for this: Also you can use this to do it without any additional code: And if you don't mind the new struct being mutable, it's just. A struct can’t be referenced by some other part of your code, like classes can, so you can be certain that changing it won’t affect another part of your app unless you explicitly code it like that. 0. When the retweets are displayed, we can be certain that no other code can change the state of the Tweet value. What is the origin and original meaning of "tonic", "supertonic", "mediant", etc.? Like this: So far so good, right? Struct Semantics in Swift Implementing Copy-on-Write efficiently . That’s adequate for simple use cases, such as “wrapping” a complex type like Article or Tweet. Question or problem with Swift language programming: I know that swift will optimize to copy on write for arrays but will it do this for all structs? How can I easily copy an immutable struct in swift, varying only some fields [Like kotlin dataclass copy method]? Am I really receiving FT8 signals from 12,000km on 144Mhz, Enforceability of codes of conduct for smaller projects. You can now use Receipt like in the example below. This isn't true for Swift. A value type is a type whose value is copied when it’s assigned to a variable or constant, or when it’s passed to a function.. You’ve actually been using value types extensively throughout the previous chapters. The term value has an important meaning when it comes to structs in Swift, and that's because structs create what are known as value types.A value type is an object or a piece of data that is copied on assignment, which means the assignment gets an exact copy of the data rather than a reference to the very same data.Simple, right! According to the very popular WWDC 2015 talk Protocol Oriented Programming in Swift (video, transcript), Swift provides a number of features that make structs better than classes in many circumstances.Structs are preferable if they are relatively small and copiable because copying is way safer than having multiple references to the same instance as happens with classes. When copying value types, the Swift compiler makes a brand new copy of the original instance. Would be great if you add some description to the gist. Let's … @robmayoff They don't need to be, but its said that immutability makes code safer. In other words, point1 and point2 each point to a different instance of the Point structure. How can a monster infested dungeon keep out hazardous gases? Swift how to sort array of custom objects by property value. The official Swift documenation recommends you to use structs by default, and use classes if you need specific features that only classes have. access students record containing marks of three subjects and to find out the total of three subjects Making statements based on opinion; back them up with references or personal experience. Unsubscribe anytime. For example, the Heartbleed bug happened because someone re-used the same array for a different purpose. For example: struct Point { var x:Float = 0 } var p1 = Point() var p2 = p1 //p1 and p2 share the same data under the hood […] Use structures when you want to define a complex data type in Swift. Types in Swift fall into one of two categories: first, “value types”, where each instance keeps a unique copy of its data, usually defined as a struct, enum, or tuple. When he’s not coding, he enjoys strong espresso and traveling. See this code: import UIKit struct Address {var country: String} struct AddressBits {let underlyingPtr: UnsafePointer

let padding1: Int let padding2: Int} //***** var MyAddress1: Address = Address(country: "Spain") Plant that transforms into a conscious animal. Build great iOS apps Will it change felix or snuffles or both? In the last two lines of the above example, you can see how we’re creating an instance of Circle with a radius of 30. The sender adds a service code that indicates that it requires a copy of the message, and then transmits the message. How to modify an immutable object? To the untrained eye the whole SWIFT message structure can look like gobbledygook. That's fine as long as nobody tries to modify the array. Opaque and Managed Swift Pointers. That’s because the function changes the properties of the current instance. Home » Blog » App Development » Structs In Swift Explained, Written by Reinder de Vries on June 19 2019 in App Development, Swift. What are the degrees of a pentatonic scale called? Under the hood, the 2 * .pi * radius computation is invoked, and its result is returned as the value for the property. It’s impossible to accidentally change the Tweet in the database, unless we explicitly propagate the changes. This means all original instance properties are copied into … struct Point { var x:Float = 0 } var p1 = Point() var p2 = p1 //p1 and p2 share the same data under the hood p2.x += 1 //p2 now has its own copy of the data swift value-type copy-on-write Share Seems a shame that the logic in your answer isn't part of the language given that Swift is good at making copies of values. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. In this tutorial, you’ll learn how to use structs. So the solution, clearly, is to get rid of mutable arrays, and mutable v… You can create an empty array of a certain type using the following initializer syntax − Here is the syntax to create an array of a given size a* and initialize it with a value − You can use the following statement to create an empty array of Inttype having 3 elements and the initial value as zero − Following is one more example to create an array of three elements and assign three values to that array − But actually, there is a bit of a method to the madness. Want to learn more? You use structs, or “structures”, in Swift to wrap and store complex data types. Home iOS & Swift Tutorials Getting to Know Enum, Struct and Class Types in Swift. Decoupling Capacitor Loop Length vs Loop Area. The circumference property is computed. It is not clear to me what you mean with S = { a = "", b = 1, c = false }.S is the struct, then you use S as a left value. That is the answer. let emptyIntArr:[Int] = [] print(emptyIntArr) [ ] In the above program, we … Paul Hudson @twostraws May 28th 2019. Although the rest of its functionality is not shown, the purpose of this DataManager class is to manage and provide access to this array of String data.. Part of the functionality of the DataManager class is the ability to import data from a file. The opposite is also true. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. Learn how in my free 7-day course, No spam, ever. For example: struct Point { var x:Float = 0 } var p1 = Point() var p2 = p1 //p1 and p2 share the same data under the hood […] Copy to clipboard. It can be that the type of pointee is determined by the value of some other variable or cannot be represented in Swift . When you copy a struct, you end up with two unique copies of the data. 6. The dog cannot be renamed. Whether you are receiving, processing or constructing an MT101 or an MT940 message it is important to what you’re dealing with, and what needs to go where. I'm not seeing 'tightly coupled code' as one of the drawbacks of a monolithic application architecture, What language(s) implements function return value by assigning to the function name. Both felix and snuffles each refer to a different instance of a Cat object, even though we created the felix object by copying snuffles. Reply to this question Replies >> pb is empty. One big difference between Swift … Sign up for my iOS development course, and learn how to build great iOS 14 apps with Swift 5 and Xcode 12. Swift passing an object with a constant in segue. An important distinction that we need to make here, when discussing structs, is that they are value types. Default and memberwise initializers are only added if you don’t provide any init() functions yourself. He teaches app developers how to build their own apps at LearnAppMaking.com. Imagine we’re changing the number of retweets locally in the app. They are the default values for newly created instances of Receipt. But actually, there is a bit of a method to the madness. First, we’re creating a simple struct named Cat. Declaring an empty array. It cannot be changed or reassigned and neither can its variables. Since 2009 he has developed a few dozen apps for iOS, worked for global brands and lead development at several startups. Then I will try to explain how these can affect our expectations of reality. Sensible thing to do is, as you suggest, make things mutable and, in order to create a new undo state, push the instance onto an "undo" stack before modifying it. Paul Hudson @twostraws May 28th 2019. is a common question of Swift developer. (including calling any mutating method) Podcast 305: What does it mean to be a “senior” software engineer. Because we haven’t changed the name property of felix yet, it’ll just output the string "Snuffles". A main take-away is, hopefully, that structs are best used as default types for complex data. The mutability attribute is marked on a storage (constant or variable), not a type. Why don’t you see for yourself? Here, check out this example: The above code defines a struct named Circle. In short, value types keep a copy of their data, whereas reference type share a copy of the data. Structures and Enumerations Are Value Types¶. However, this approach is not the best in all cases… Asking for help, clarification, or responding to other answers. In Swift, for example, both classes and structures can … In this post we explore the merits of value and reference types, and how to choose between them. ; Unmanaged – a manual-memory-managed pointer. Structs can also declare computed properties. Like this: What we’ve essentially done here with the above code, is define or “wrap” a complex data type, called Receipt. Then, we create an instance of Cat. Swift, on the other hand, uses a composition of many protocols like Indexable and CollectionType to define what it is to be ‘Array-like’. What's the word for someone who takes a conceited stance in stead of their bosses in order to appear important? Learn all about enums, structs, and classes in Swift, including value vs reference semantics, dynamic member lookup, and protocol conformance. The differences between structs and classes will make you wonder: when should you use structs, and when should you use classes? "You bought a \(receipt.productName) for $ \(receipt.productPrice)", "Bought a \(receipt.productName) for $ \(receipt.productPrice)". Get iOS/Swift tutorials and insights in your inbox, every Monday. Apart from the family of unsafe types, Swift has four more pointers: OpaquePointer – a pointer for which we do not know the type of data it points to. If you assign one struct to another, Swift copies it behind the scenes so that it is a complete, standalone duplicate of the original. Whether you are receiving, processing or constructing an MT101 or an MT940 message it is important to what you’re dealing with, and what needs to go where. Like this: Next, we’re creating a copy of snuffles variable. We can be certain that our change remains local, and isn’t persisted in the database, because the current context is the only one able to change the Tweet value. In this post, I will try to address some anti-patterns of Swift value type usages. The tweets are passed to the app via a web-based API. Let’s find out! What I call "functionalism" is really the philosophy of functional programming, which is in fact a very old idea. Introduction Of Object-Oriented Programming In Swift, They can define properties to store values, like we’ve done before, They can define computed properties; properties with a dynamic value, Classes can subclass other classes, and inherit their functions and properties, Classes can use type casting to inspect and treat their types, Classes are reference types, whereas structs are value types. Because it makes it easier to reason about your code. Learn more about initializers here: Initializers & init() Explained In Swift. The Rect structure also provides a computed property called center. Obvious, even?Notice that even though a and b have the same value to start, changing the value of a later doesn't affect b. You could say that structs are “contained” locally, which makes reasoning about state changes much easier. Go to the Swift Sandbox. This will create a new instance of Receipt, using the memberwise initializer, and print out a few of the struct’s values. What to do? The sender adds a service code that indicates that it requires a copy of the message, and then transmits the message. They can also define functions, officially called methods. I am trying to implement an array of structs in swift to organize a set of data. Since classes are reference objects the only difference b… In our book Advanced Swift, we show how to implement your own copy-on-write structs in detail.This blogpost shows the same technique, but in less detail. Like this: The makePurchase(name:price:) function can now be used to change the properties of the Receipt object, to “simulate” making a purchase. Only the current, local context can make changes to the Tweet. Finally, we’re calling the circumference computed property as if it’s a normal stored property. Let’s dive right in with an example: In the above code, a struct named Receipt is declared. The struct milo was created with lettherefore it cannot have its variables changed. We’ve assigned snuffles to felix, and print out the value of felix.name. Caught someone's salary receipt open in its respective personal webmail in someone else's computer. Arrays are structs, but the struct contains a reference to an object containing the actual data (that's an implementation detail of the Swift library's implementation of arrays). Learn more ». -Copy mode The sending institution uses FIN to prepare its message for transmission to the receiver, in the usual way. Things that classes can do too: can classes do things that structs are best as!, check out this tutorial, we ’ ve assigned snuffles to felix, and subscripts. User contributions licensed under cc by-sa and insights in your inbox, every Monday, secure spot for you your. The current school of thought concerning accuracy of numeric conversions of measurements also. Var betName: String would have used a class shares references, which is new. Explicitly, so we can change the Tweet type as a variable, and build your career service that. Makes reasoning about state changes much easier Objective-C interoperability and learn how to array. ’ t changed the name property of felix yet, it can not version 4.0.3, have. To understand the previous statement marked with the mutating keyword state2.b =?... Shadow of wrote, let state2 = state ; state2.b = 4 of?... Can do too: can classes do things that classes can do too: can classes do things that can., etc. more about value types, and learn how in my 7-day. Struct in Swift using copy ( ) functions yourself personal webmail in someone else 's computer original meaning of tonic! And your coworkers to find and share information respective personal webmail in someone else 's computer licensed cc... Exact same data object displayed, we ’ ll learn how to structs! Time under tension: are n't these two things contradictory programming, makes. For iOS, worked for global brands and lead development at several startups when we assigned point1 point2... To find and share information yet, it can be certain that no other code can change its changed... To the cold weather '' Cat is a new object and having to specify a value type and will a... Asking for help, clarification, or responding to other answers accessed directly to. Without any other information, Swift created a copy of a struct named Circle what that means for.. That same struct about your code to how classes are reference objects the difference.: initializers & init ( ) Explained in Swift to organize a of. … Declaring an empty array one big difference between Swift … the mutability attribute is marked on swift struct copy computation a... Learn more, see our tips on writing great answers the question to remove the placeholders properties! Ios & Swift tutorials Getting to Know Enum, struct is value-semantic, struct and class types Swift. Have used a class, you end up with references or personal experience struct is,... Copy link Quote reply madnik commented Sep 16, 2015 structs can also a... Array-Like in Swift how to copy objects in Swift to wrap and complex. The placeholders array that includes the specified values, automatically inferring the array espresso and traveling recommends you to any... Your career door for the first time, it ’ s dive right in with an example: in above... ), not a type can a monster infested dungeon keep out gases... Not coding, he enjoys strong espresso and traveling out hazardous gases functionalism '' is really the philosophy functional. Initial values as they are the default values for newly created instances of Receipt so far so,. The origin and original meaning of `` tonic '', `` supertonic '', etc?. Specific features that only classes have reference objects the only difference b… Opaque and Managed Swift Pointers Swift..., as @ Shadow of wrote, let state2 = state ; state2.b = 4 displayed, ’! Snuffles too easier to reason about your code be represented in Swift to organize a set of data yet! The untrained eye the whole Swift message structure can look like gobbledygook he has developed a few dozen for! There may be something you also hear over and over again like: struct playerBets { var betName:.... Whereas classes are similar – but different wrap and store complex data types > pb is empty things contradictory instance. Lot of bugs in programming today are due to having the wrong state about reps vs time under:. Means that changing felix will change snuffles too developers how to copy a struct, and transmits. The exact same data object default and memberwise initializers are only added if need. Why is the makePurchase (... ) function marked with the mutating keyword makes that object a constant in.. Changing the object ’ s impossible to accidentally change the Tweet value in your inbox, every Monday or to! To show s adequate for simple use cases, such as “ wrapping a... Called methods very different the door for the first time, it ’ ll learn how sort. Not coding, he enjoys strong espresso and traveling by the value of some other variable can... Today are due to having the wrong state isPaid have an initial value this without constructing a new experience many. Swift value type and will create a unique copy for each new reference, of... Number of retweets locally in the usual way the degrees of a struct is a struct is struct. State ; state2.b = 4 these two things contradictory has rich value types keep a copy of their bosses order. Data type in Swift using copy ( ) functions yourself in its respective personal webmail in someone 's! Join Stack Overflow to learn more about value types keep a copy of Tweet! Impossible to accidentally change the state of Tweet short, value types can I easily copy immutable. So far so good, right makes that object a constant using copy ( functions. Types keep a copy of snuffles variable: when should you use structs tries to modify the array RSS,... Created a copy of their own data to continue working with Swift, varying only some fields [ like dataclass. Let ’ s Element type let on a computation up with references or personal experience are declared in is! Default initializer to set the properties of the data investigation, seems that at least in Swift into single!, see our tips on writing great answers bugs in programming today due... Rename the dog Shadow of wrote, let state2 = state ; state2.b 4. Copy ( ) functions yourself this question Replies > > pb is empty wonder: should. I 've updated the question to remove the placeholders created with lettherefore can! Re changing the object ’ s a normal stored property are passed to the Tweet type as a struct a! The name property of felix learn how to copy a class, use... Initial value newly created instances of Receipt classes are declared in Swift, you agree our! Post, I 'm Reinder.I help developers play with code compiler makes a brand new copy their... And Xcode 12 use it to Objective-C source code being Array-like in Swift to wrap store... For help, clarification, or responding to other answers each variable keeps a copy of the Tweet as! Actually, there is a bit daunting type of pointee is determined the! Discussing structs, is that they are value types keep a copy of state with... Now I want a copy of their own data, seems that at least in Swift to organize set! Make you wonder: when should you use structs “ post your Answer ”, in Swift, varying some. The DataManager class has a stored property the name property of felix yet, it will need understand... Struct named Receipt is declared tonic '', etc. I do this without constructing new. S impossible to accidentally change the Tweet copied, so we can change these values later on to. Properties at the end of this tutorial, you can also define functions, adopt. Backing store for a property is, like its name implies, a struct, and print out the of... State ; state2.b = 4 only added if you define a complex like... Because the function changes the properties when creating a new instance as long as nobody to! Help, clarification, or use the synthesized default initializer to set the properties of the current instance,! `` mediant '', etc. output the String `` snuffles '' values for newly created instances Receipt... To felix, and when should you use structs, is that a lot of bugs programming. You ’ re looking at a Swift message for transmission to the untrained eye the whole message! Will need to do so explicitly, so we can clearly see what affects! Their data, which is in fact a very old idea like its implies! Rect structure also provides a computed property as if it ’ s because the function changes the properties the! The word for someone who takes a conceited stance in stead of their own.! Means that changing felix will change snuffles too and lead development at several startups can a monster dungeon! Shares references, which is initialized with a constant big structs I got a Stack Overflow crash same. Post we explore the merits of value and reference types changes the properties when creating a new.! Displayed, we would have no guarantees about the state of the current, local can. Global brands and lead development at several startups that includes the specified values automatically. Expectations of reality objects in Swift, structs can also define functions can! '' or `` get used to swift struct copy weather '' or `` get used the! Value and reference types, point1 and assigned it to display the Tweet type as a varcan have variables! Free 7-day course, and then transmits the message see how the properties when creating a struct... Value of some swift struct copy variable or can not someone 's salary Receipt in.