Скачать или смотреть Fixing the Swift Error: Cannot use mutating member on immutable value: 'self' is immutable

Learn how to resolve the "Cannot use mutating member on immutable value" error in Swift. This guide provides a clear solution to help you fix your code efficiently.
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Fixing the Swift Error: Cannot use mutating member on immutable value: 'self' is immutable

In the world of Swift and SwiftUI, encountering errors can be frustrating, especially when they're confusing. One such common error is the Cannot use mutating member on immutable value: 'self' is immutable. If you've stumbled upon this while coding, particularly while working with a SwiftUI view, you are not alone. Many developers face this issue, especially when working with state and trying to mutate properties of a view.

Understanding the Error

The heart of the error lies in how SwiftUI handles views. In SwiftUI, structs are value types, meaning they are immutable by default. When you attempt to mutate a property of a struct, like you're trying to do with self in the following line:

[[See Video to Reveal this Text or Code Snippet]]

You run into the error because Swift believes that you are trying to change an immutable value.

Quick Disclaimer

Before we delve into the solution, it’s essential to understand that modifying properties directly within a View struct like this is against SwiftUI's principles. The SwiftUI framework encourages a unidirectional data flow and often requires the use of @ State or other property wrappers for mutability.

Solution: Using @ State for Mutability

The solution is quite straightforward! The properties that you want to mutate need to be declared as @ State. This will allow SwiftUI to recognize that these properties can change over time. Here’s how you can modify your code accordingly:

Step-by-Step Code Modification

Declare Mutable Variables as @ State: Change your array declarations to be @ State properties.

Adjust the prepareConfetti Function: Change the mutating function to a regular non-mutating function, as you won’t need it to mutate the state anymore.

Here's how you can refactor your code:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Explained:

@ State: Adding @ State to the arrays allows them to be mutable within the SwiftUI view, handling state changes efficiently.

Removed mutating: The mutating keyword was removed from prepareConfetti since we are now using state properties.

Conclusion

Resolving the Cannot use mutating member on immutable value: 'self' is immutable error is essential for smooth development in SwiftUI. By following the steps outlined above, you can leverage SwiftUI’s state management features to ensure that your views respond dynamically to changes. Moving forward, remember to use @ State whenever you plan to mutate properties within a SwiftUI view to avoid similar issues. Happy coding!