conditional assignment swift

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Conditionals & Logic

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if Statement

An if statement executes a code block when its condition evaluates to true . If the condition is false , the code block does not execute.

else Statement

An else statement is a partner to an if statement. When the condition for the if statement evaluates to false , the code within the body of the else will execute.

else if Statement

An else if statement provides additional conditions to check for within a standard if / else statement. else if statements can be chained and exist only after an if statement and before an else .

Comparison Operators

Comparison operators compare the values of two operands and return a Boolean result:

• < less than
• > greater than
• <= less than or equal to
• >= greater than or equal to
• == equal to
• != not equal to

Ternary Conditional Operator

The ternary conditional operator, denoted by a ? , creates a shorter alternative to a standard if / else statement. It evaluates a single condition and if true , executes the code before the : . If the condition is false , the code following the : is executed.

switch Statement

The switch statement is a type of conditional used to check the value of an expression against multiple cases. A case executes when it matches the value of the expression. When there are no matches between the case statements and the expression, the default statement executes.

switch Statement: Interval Matching

Intervals within a switch statement’s case provide a range of values that are checked against an expression.

switch Statement: Compound Cases

A compound case within a switch statement is a single case that contains multiple values. These values are all checked against the switch statement’s expression and are separated by commas.

switch Statement: where Clause

Within a switch statement, a where clause is used to test additional conditions against an expression.

Logical Operator !

The logical NOT operator, denoted by a ! , is a prefix operator that negates the value on which it is prepended. It returns false when the original value is true and returns true when the original value is false .

Logical Operator &&

The logical AND operator, denoted by an && , evaluates two operands and returns a Boolean result. It returns true when both operands are true and returns false when at least one operand is false .

Logical Operator ||

The logical OR operator, denoted by || , evaluates two operands and returns a Boolean result. It returns false when both operands are false and returns true when at least one operand is true .

Combining Logical Operators

Logical operators can be chained in order to create more complex logical expressions. When logical operators are chained, it’s important to note that the && operator has a higher precedence over the || operator and will get evaluated first.

Controlling Order of Execution

Within a Swift logical expression, parentheses, () , can be used to organize and control the flow of operations. The usage of parentheses within a logical expression overrides operator precedence rules and improves code readability.

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Conditional statements

Sometimes you want code to execute only if a certain condition is true, and in Swift that is represented primarily by the if and else statements. You give Swift a condition to check, then a block of code to execute if that condition is true.

You can optionally also write else and provide a block of code to execute if the condition is false, or even else if and have more conditions. A "block" of code is just a chunk of code marked with an open brace – { – at its start and a close brace – } – at its end.

Here's a basic example:

That uses the == (equality) operator introduced previously to check whether the string inside person is exactly equivalent to the string "hater". If it is, it sets the action variable to "hate". Note that open and close braces, also known by their less technical name of "curly brackets" – that marks the start and end of the code that will be executed if the condition is true.

Let's add else if and else blocks:

That will check each condition in order, and only one of the blocks will be executed: a person is either a hater, a player, or anything else.

Evaluating multiple conditions

You can ask Swift to evaluate as many conditions as you want, but they all need to be true in order for Swift to execute the block of code. To check multiple conditions, use the && operator – it means "and". For example:

Because stayOutTooLate and nothingInBrain are both true, the whole condition is true, and action gets set to "cruise." Swift uses something called short-circuit evaluation to boost performance: if it is evaluating multiple things that all need to be true, and the first one is false, it doesn't even bother evaluating the rest.

Looking for the opposite of truth

This might sound deeply philosophical, but actually this is important: sometimes you care whether a condition is not true, i.e. is false. You can do this with the ! (not) operator that was introduced earlier. For example:

This time, the action variable will only be set if both stayOutTooLate and nothingInBrain are false – the ! has flipped them around.

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Use if/else and switch statements as expressions in Swift 5.9

Swift 5.9 brought an arsenal of enhancements to the already powerful and versatile language, but there's one in particular that has been long anticipated by developers. Swift now allows the use of if/else and switch statements as expressions, presenting an avenue to write more readable and concise code. This feature is a game-changer in initializing variables based on complex conditions without resorting to difficult-to-read ternary expressions.

If/Else Statements as Expressions

Consider the situation where you want to initialize a let variable based on a complex condition. Traditionally, this would necessitate using compound ternary expressions that can quickly become convoluted. Here's an example of what that may look like:

Now, with Swift 5.9, you can leverage if/else expressions. This allows you to use a more familiar and readable chain of if statements. Below is the transformed code:

The updated code is considerably more readable and easier to follow, enhancing the overall maintainability of the codebase.

Global Variables and Stored Properties

The ability to use if/else and switch statements as expressions is particularly useful when initializing a global variable or a stored property. In previous versions of Swift, if your initialization required complex conditionals or switch statements, you would need to wrap them in a closure and execute it immediately, as shown:

Now, with the power of if expressions, you can simply eliminate that clutter, leaving you with much neater code:

Swift 5.9 brings a significant enhancement in readability and conciseness by allowing if/else and switch statements to be used as expressions. This can drastically improve your code structure, making it easier to read, understand, and maintain.

Happy coding!

XOXO, Christian 👨🏻‍💻

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Conditional compilation within Swift expressions

• language features

New in Swift 5.5: It’s now possible to conditionally compile postfix member expressions using Swift’s #if compiler directive . Let’s take a look at what kinds of situations that this new feature could be really useful in.

Working around platform differences

Although many of the built-in APIs and frameworks work exactly the same way across Apple’s platforms, there are certain differences that we might need to work around. For example, when using SwiftUI to build an app that runs on both iOS and the Mac, we might find ourselves in the following type of situation — in which we’re getting an error when attempting to apply the iOS-specific InsetGroupedListStyle to a List :

In general, these kinds of issues can be worked around using a compile-time platform check — but before Swift 5.5, we’d have to first break our List out into a separate expression, and then apply different listStyle modifiers separately using an #if -based operating system condition:

In isolation, the above code doesn’t look that bad , but if our ItemList view were to gain additional subviews (or if we’d need to perform additional compile-time checks within it), then its body could quickly become quite hard to read.

So perhaps a more robust solution to this problem would be to instead extract the above platform check into a dedicated modifier method — for example like this:

With the above in place, we can simply apply our new defaultListStyle modifier within our ItemList view, and we no longer have to deal with any platform differences when constructing our actual UI:

However, while the above is certainly a neat technique when working with modifiers and styles that we’re looking to reuse multiple times across a project, always having to define a dedicated method each time we encounter a platform difference can become quite tedious.

This is where Swift 5.5’s new support for #if conditions within postfix member expressions comes in.

Inline checks within expressions

When using Swift 5.5, we now have the option to inline #if directives right within our expressions. So, going back to our ItemList , we can now conditionally apply each of our listStyle modifiers completely inline — without first having to break our expression up into multiple parts:

Above we’re also making use of another new language feature that enables us to refer to SwiftUI list styles (and other kinds of protocol-based types) using dot syntax. Check out “Using static protocol APIs to create conforming instances” to learn more about that.

Nice! Of course, this new capability also works for other kinds of #if -based compile-time checks — including using the standard DEBUG flag to check if our app is being compiled using its debug build configuration, and any custom compiler flags that we might’ve defined.

As an example, here’s how we could use a custom flag to conditionally visualize the final rendering size of one of our views:

To learn more about how to define and use custom compiler flags, check out “Using compiler directives in Swift” .

So, how should we pick between these new inline #if conditions versus creating dedicated modifiers for working around platform differences and for performing other kinds of compile-time checks? While every developer will certainly have their own preferences — for me, it all depends on whether a given pattern will be repeated within a code base, or whether it’s something that we’re only performing once.

For repeated compile-time checks, I still prefer to create dedicated functions, since that lets me wrap those checks up into a much simpler API, but when working around minor platform differences (like we did above), I prefer the new inline style. It’s already proving to be quite useful when working on cross-platform SwiftUI-based projects.

If you have any questions, comments, or feedback, then feel free to reach out via email .

Thanks for reading!

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Swift Conditional Statements

Swift Conditional Statements are those which execute a block of code based on the result of a condition or boolean expression.

Swift supports following conditional statements.

• Swift If Statement
• Swift If-Else Statement
• Swift Switch Statement

We can use Logical Operators to form compound conditions. The following tutorials cover some of the scenarios where logical operators are used in conditions of Swift Conditional statements.

• Swift If with AND Operator
• Swift If with OR Operator
• Swift If with NOT Operator

The following cover some of the conditional statements in Swift Programming.

If Statement

In the following example, we take an integer a = 10  and check if variable a is less than 20 . Since the condition evaluates to true , the statements inside the if block execute.

If-Else Statement

In the following example, we take an integer a = 30  and check if variable a is less than 20. As the expression evaluates to false, the statements inside the else block execute.

Switch Statement

In the following example, we have a simple expression with two variables. We have case blocks with values 4, 5, 6 and default. When the expression’s value matches any of the values, corresponding block is executed.

In this Swift Tutorial , we have learned about conditional statements in Swift Programming.

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This tutorial belongs to the Swift series

if statements are the most popular way to perform a conditional check. We use the if keyword followed by a boolean expression, followed by a block containing code that is ran if the condition is true:

An else block is executed if the condition is false:

You can optionally wrap the condition validation into parentheses if you prefer:

And you can also just write:

One thing that separates Swift from many other languages is that it prevents bugs caused by erroneously doing an assignment instead of a comparison. This means you can’t do this:

and the reason is that the assignment operator does not return anything, but the if conditional must be a boolean expression.

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A ternary operator can be used to replace the if...else statement in certain scenarios.

Before you learn about the ternary operator, make sure to know about Swift if...else statement .

• Ternary Operator in Swift

A ternary operator evaluates a condition and executes a block of code based on the condition. Its syntax is

Here, the ternary operator evaluates condition and

• if condition is true , expression1 is executed.
• if condition is false , expression2 is executed.

The ternary operator takes 3 operands ( condition , expression1 , and expression2 ). Hence, the name ternary operator .

• Example: Swift Ternary Operator

In the above example, we have used a ternary operator to check pass or fail.

let result = (marks >= 40) ? "pass" : "fail"

Here, if marks is greater or equal to 40 , pass is assigned to result . Otherwise, fail is assigned to result .

• Ternary operator instead of if...else

The ternary operator can be used to replace certain types of if...else statements. For example,

You can replace this code

Here, both programs give the same output. However, the use of the ternary operator makes our code more readable and clean.

• Nested Ternary Operators

We can use one ternary operator inside another ternary operator. This is called a nested ternary operator in Swift. For example,

The number is Positive.

In the above example, we the nested ternary operator ((num > 0) ? "Positive" : "Negative" is executed if the condition num == 0 is false .

Note: It is recommended not to use nested ternary operators as they make our code more complex.

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Very often developers need to build dictionaries from optional values. Sure, it’s pretty easy to do it in Swift , right? It’s just [ String: Any? ]  , so why write a blog post about it? We will use it as one of our use cases for our handy conditional assignment operator.

So let’s look at an example from a real life project - Zonky. The app presents a screen where you can select multiple loan parameters to filter the list of loans. 

All of these parameters are optional of course. In order to apply the selected filters, we need to send the parameters to a server as a dictionary. A filtering function with the dictionary can look like this:

It seems to be OK, but we don’t want optionals in our dictionary because Alamofire takes [ String: Any ]   as a type of parameter dictionary. How do we fix that? The most straightforward solution is pretty obvious:

Fine, it works, but imagine a larger set of parameters. That’s a lot of ugly and boring code! ? That’s what leads us to the idea behind our conditional assignment operator. We want to assign a value to the dictionary only if it’s not nil.

Voilà. Shorter, nicer, more readable ? But it’s not the standard operator included in Swift, so let’s look at how it works under the hood. The basic idea is simple- we just moved the unwrapping and assignment code used in the second example to the custom operator definition.

And that’s it! We have a small piece of code which makes our codebase much nicer. You can use this operator not only for building dictionaries (there are other and maybe even smarter ways to achieve this) but whenever you need to assign value only if it’s not nil, and trust me, it’s a very common case, and you will like it ?

If you like this simple trick, see our ACKategories - lightweight open source library full of similar useful tools and extensions, or just wait for our next blog posts, and we will show you more recipes from our kitchen ?‍?

• Conditional assignment operator

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Syntactic sugar for assigning Optional values and conditional assignment

Hi Team! I hope you are doing well. I'm sorry for such a minor ideas but for my project they will make code more compact.

• Assigning optional only if it has a value. E.g.: var a: Int? var b = 0 instead of: if (a != nil ) { b = a } use short: b =? a I can do it by implementing a custom operator but I think it's good to have it in the standard library: infix operator =? : AssignmentPrecedence extension Int { static func =?(left: inout Int, right: Int?) { if right != nil { left = right! }} }
• The second idea for the conditional assignment I don't know how to implement by myself. E.g. let c = 0 var d = 0 we have a ternary operator for the case when we want to assign an alternative value in case some condition is false: d = c > 0 ? c : 1 but if we don't want to use any alternative then we need to write code like this: if (c > 0) { d = c } My suggestion is to simplify the syntax somehow. E.g.: d = c > 0 ? c or d = c > 0 ? c : _ I understand that the proposals are looking as they're out of thin air, but when you are reading dozens of parameters from the external source it's good to make it as short as possible.

Thank you in advance!

Best regards, Vsevolod Migdisov

You can also do b = a ?? b

(it’s not quite the same as in b will be reassigned if a is nil , but the end result is the same i.e b will either contain the value stored in a or 0 )

I think this is just d = max(c, 1) .

Similarly, you can write this as d = max(c, d) , although I prefer the original.

Do you have any other examples where the syntactic sugar for ternary operations might offer an improvement? Syntactic sugar additions have a very high bar for entry into the language.

I do the same in my code for both proposals - if condition is false then I assign the variable itself. But I think it looks not quite elegant: b = a ?? b d = c > 0 ? c : d

Both proposals are not just for Int. It can be applied to String as well or any other types: if (str != "") { str = "some string") The idea is that if the condition is false then no assignment should be done. The same as in the 1st proposal - if the value is nil then don't do the assignment at all.

Okay. It looks like the =? change has been pitched before and rejected, so I’m not sure if it’s worth pursuing.

The other change you mentioned doesn’t look like it’s been pitched before, so perhaps you can just focus on that.

I personally don’t see a need to optimize the syntax for if (c > 0) { d = c } as I think it is perfectly fine to write and is readable.

Thanks a lot, Suyash!

Swift requires braces for all if statements, so parentheses aren't needed like they are in other languages.

I've found both solutions for myself but I still think it's good to have it in the standard library: infix operator ?= : AssignmentPrecedence func ?=< T >(lhs: inout T, rhs: T?) { if rhs != nil { lhs = rhs! } } func ?=< T >(lhs: inout T, rhs: (Bool, T)) { if rhs.0 { lhs = rhs.1 } }

No please don't use map for side-effects! There should be a forEach but for optionals, but until we have that please let's all keep map functional!

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PetrusM commented Mar 3, 2023 • edited Loading

?= : Assignment is performed only if the variable (left side) is null - it does not crush any value. =? : Assignment is performed only if the new value (right side) is not null.

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Single line if statement in Swift

How would one convert the following to Swift from Objective-C?

Swift does not use parentheses around the conditional, however the following code gives an error.

• objective-c

• 7 Unlike Objective C, braces are mandatory while using if statements in Swift. The reason behind this is to make the code safer. –  ZeMoon Commented Jun 11, 2014 at 9:01
• you have to add the braces {} for all branches, but the parenthesis are optional () , you can keep them if you'd like to. –  holex Commented Jun 11, 2014 at 12:59

8 Answers 8

Well as the other guys also explained that braces are a must in swift. But for simplicity one can always do something like:

In Swift the braces aren't optional like they were in Objective-C (C). The parens on the other hand are optional. Examples:

Valid Swift:

Invalid Swift:

This design decision eliminates an entire class of bugs that can come from improperly using an if statement without braces like the following case, where it might not always be clear that something 's value will be changed conditionally, but somethingElse 's value will change every time.

• 7 One example of a widely publicized bug which is related to this, is Apple's SSL/TLS bug , while Swift was in development. I sometimes wonder if this design decision was made because of that, or if it's just coincidental. It's an interesting detail of Swift, since it's very uncommon for "C like" languages to enforce a coding style. –  Jonas Commented Feb 5, 2015 at 12:29
• Apple's SSL/TLS bug - doesn't indicate that single line If's are the problem. It clearly shows that CMD+V should not use "Key-delay" and "key-repeat" setting of keyboard and should paste only once. Try copying one line of text and press CMD+V a little longer than usual. That's unless, developer purposely put two consecutive "goto fail;" assuming to work in a single if block, to make sure that if in case the control pointer does not obey the first time, repeating a second time would help. "You still here ???? I have already told you to goto fail.... GOTO FAIL this instant !!!" –  Nikhil Mathew Commented Aug 2, 2016 at 19:10
• You can't put parenthesis around if let statements. –  Iulian Onofrei Commented Nov 30, 2017 at 22:36

You can use new Nil-Coalescing Operator, since Swift 3 in case when you need just set default value in case of if fails:

In case if someOptional is false , this operator assign "" to someValue

One-line if , one-line while and one-line for are considered a bad style by many developers because they are less readable and allegedly a source of many errors.

Swift solved the conundrum by forbidding one-line flow control statements; the braces are non-optional...

Of course, you can still do

There are also implementation reasons. Having the parentheses around the condition as optional makes the parsing much harder. Enforcing braces simplifies parsing again.

• "Alleged" is about right. With conventions such as consistent use of Allman braces and indentation, it was already very preventable. –  Peter DeWeese Commented Jul 26, 2014 at 1:45

Here is a simple solution I used in my projects.

One line solution for Swift 3+

Swift 5 Easy One line Solution

• 1 I think swift conventions says to not use parenthesis on if statements –  Javier Heisecke Commented Oct 7, 2021 at 15:58

Swift 5 Easy Solution

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