Скачать или смотреть How to Make Dictionary Array Values Mutable in Swift

Discover a simple and efficient solution to making dictionary array values mutable in Swift without unnecessary copies or lookups.
---
This video is based on the question https://stackoverflow.com/q/77596160/ asked by the user 'Thomas Tempelmann' ( https://stackoverflow.com/u/43615/ ) and on the answer https://stackoverflow.com/a/77596194/ provided by the user 'Joakim Danielson' ( https://stackoverflow.com/u/9223839/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Swift: Making dictionary array values mutable

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Make Dictionary Array Values Mutable in Swift

When developing applications in Swift, you may encounter scenarios where you need a mutable dictionary whose values are arrays. This is a common coding pattern, especially for those familiar with other programming languages like Objective-C. The challenge arises when you try to manipulate these array values—specifically, the behavior you might expect does not always manifest as anticipated.

The Problem

Consider this code written in Swift 5:

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

In the above code, an array is expected to be appended with values and reflect those changes inside the dictionary. However, it prints an empty array due to Swift’s value semantics. When you retrieve the array from the dictionary, you're actually working with a copy of the original array instead of a direct reference. This leads to confusion because modifying ints does not update intsForString[forKey].

The Solution: Using Default Values

Fortunately, there is a straightforward solution that retains efficiency and avoids handling unnecessary copies. Rather than checking if the value exists and modifying it separately, you can directly append to the array in the dictionary using:

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

Explanation

Let’s break down the solution:

Use Default Values: The key concept here is using the default parameter in the subscript. This allows you to specify a default value (an empty array [] in this case) if the key doesn’t exist yet.

Simplifying the Code: By using this method, you encapsulate the logic in a single line. This not only optimizes performance by avoiding redundant lookups but also simplifies your code, making it easier to read and maintain.

Avoiding Unnecessary Copies: The use of default lets you access the array directly and append to it without needing to explicitly update the dictionary afterward. This means fewer copies and more efficient memory usage.

Final Implementation

Below is how your modified function could look while utilizing the default feature seamlessly:

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

Conclusion

In summary, if you find yourself needing mutable dictionary values in Swift, leveraging the default subscript syntax can save you from the pitfalls of value copying. Utilizing this approach allows for efficient, clear, and more maintainable code. By streamlining your additions and avoiding unnecessary key lookups, you can enhance your Swift programming experience significantly.

Remember, simplicity is key in creating maintainable code, and Swift provides elegant solutions to common challenges—make the most of them!