Скачать или смотреть Understanding Computed Property in Protocol Extensions for Swift Stacks

Discover how to fix the issue with computed properties in protocol extensions when implementing a Stack in Swift. Learn the correct approach to get the desired results.
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This video is based on the question https://stackoverflow.com/q/70739798/ asked by the user 'Tanmay Agarwal' ( https://stackoverflow.com/u/13314370/ ) and on the answer https://stackoverflow.com/a/70740056/ provided by the user 'Dávid Pásztor' ( https://stackoverflow.com/u/4667835/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Computed Property in Protocol Extensions for Swift Stacks

When you're diving into the world of Swift programming, particularly while working with protocols and extensions, you might face some unexpected behavior. One common problem arises when using computed properties in protocol extensions, especially when implementing data structures like a Stack. In this guide, we will clarify this issue and provide solutions to ensure you achieve the desired results from your code.

The Problem: Why Isn't the Count Updating?

Imagine you are implementing a Stack in Swift by creating two protocols: Container to manage a collection of items, and Stack, which inherits from Container. To monitor the number of elements in your stack, you decided to add a computed property named count to the Container. However, despite pushing an element onto the stack, your count property keeps returning 0. You might wonder, why is count not reflecting the expected value?

Here’s a snippet of your original code for reference:

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The Explanation: Understanding Stored and Computed Properties

The Fundamental Issue

The primary reason your count property is not returning the correct value is because you have declared count as a stored property in MyStack. In Swift, when a conforming type (like your MyStack) provides its own implementation for a property that is defined in a protocol, it overrides the default implementation provided by that protocol.

Solution: Remove the Stored Property

To resolve this issue, you need to remove the count property from MyStack. By doing so, the default computed property implementation in the Container protocol will take effect, and your count will accurately reflect the size of your array (arr) every time you call it.

Here’s the modified code that correctly uses the computed property:

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

Key Takeaways

Understanding Property Types: Know the distinction between stored and computed properties. If a conforming type implements a property, it will not automatically use the protocol's implementation.

Protocol Extensions: Use these effectively to provide default behavior for properties, methods, etc.

Debugging: Always double-check your property implementations when faced with unexpected results, especially when working with protocols and extensions.

Conclusion

In conclusion, when implementing your Swift Stack, remember that computed properties in protocol extensions provide a way to access dynamic values! Always ensure that anything you define in a conforming type does not conflict with default implementations unless intended. By removing the stored count property from your MyStack, you can take full advantage of the protocol's computed properties, leading to code that works as expected.

Happy coding! If you have any questions, feel free to reach out in the comments.