Скачать или смотреть How to Use Generics in Swift for Class and Protocol Conformance

Discover a simple way to use `generics` in Swift to process multiple types conforming to both a class and a protocol, avoiding common pitfalls and compiler errors.
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This video is based on the question https://stackoverflow.com/q/64937963/ asked by the user 'Richard Witherspoon' ( https://stackoverflow.com/u/10830089/ ) and on the answer https://stackoverflow.com/a/64938433/ provided by the user 'Leo Dabus' ( https://stackoverflow.com/u/2303865/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Swift Function Input: Generic Conformance Between Class and Protocol

Swift developers often encounter challenges when trying to create functions that accept types conforming to both classes and protocols. This post will explore how to effectively tackle issues related to function inputs that require both generic class and protocol conformance, particularly when dealing with arrays of objects.

The Problem: Understanding the Compiler Error

Imagine you need a Swift function that can process the values of different measurement types. Each measurement type needs to conform to a specific class, MeasurementClass, as well as a protocol, UnitDelegate. However, when attempting to use an array of types that conform to both, you might run into a compiler error:

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This means you're facing issues when passing an array of subclasses to a method expecting a parameter of a specific type.

The Original Approach: Using Protocols and Class Composition

Here’s how the original implementation looked:

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As you can see, while the individual types work well when processed through the printValues method, the array of types causes complications, leading to the mentioned compiler error.

The Solution: Simplifying with Structs and Enumerations

Instead of relying on complex class and protocol compositions, a simpler solution is to use a struct which includes an enumeration. This change significantly enhances your code's clarity and functionality.

Step 1: Define the Struct and Enumeration

Here's how you can define a struct that includes an enum to differentiate between the kinds of measurements:

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Step 2: Adding a Printing Function

Next, extend the struct to include a method for printing values:

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Step 3: Using the New Struct

Now you can create instances of AMeasurement and process them without issues:

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Output

The final output of the code prints correctly without any compiler errors:

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Conclusion

By adopting a simpler approach using a struct and enumeration, we can effectively eliminate the complications associated with generics and protocol conformance in Swift. This not only resolves the compilation issues but also makes your code cleaner and easier to understand. Embrace these strategies to enhance your Swift programming experience!