Скачать или смотреть Solving the Dart Enhanced Enum Problem with Non-Constant Values

Discover how to bypass Dart's limitations with enhanced enums and non-constant values by using classes instead.
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This video is based on the question https://stackoverflow.com/q/76810176/ asked by the user 'Pawan Acharya' ( https://stackoverflow.com/u/11707151/ ) and on the answer https://stackoverflow.com/a/76810633/ provided by the user 'Maciej Bastian' ( https://stackoverflow.com/u/14468288/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Issue with Dart Enhanced Enums

Dart's enhanced enums are a powerful feature, but they come with certain restrictions. A common issue developers encounter is the inability to use non-constant fields in enhanced enums. This post will explore this limitation and provide a clear solution.

The Problem: Non-Constant Value in Enhanced Enum

Consider the following code snippet:

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In this code, the TestEnum enum defines two values: john and doo. However, when trying to assign a non-constant variable (dynamic) to the doo enum value, an error is thrown:

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Why Does This Error Occur?

Dart requires that all generative constructors be constant and that instance variables be final. This means that you can only use compile-time constants when initializing enums.

What Happens When You Remove const and final?

You might wonder if bypassing these restrictions will solve the issue. However, simply removing const and final from the enum definition will not work. This leads to another type of error, indicating that your attempt does not conform to the language's requirements.

The Solution: Using Classes Instead

The good news is that you can achieve similar functionality to enums, but with the flexibility of using non-constant values. Instead of using enums, you can use classes.

Implementation of the Class Approach

Here is how you can implement it:

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How It Works

Factory Constructors: This uses factory constructors to create instances of the TestEnum class. You can customize each factory method to provide dynamic values.

Constant Constructor: The constructor can still be constant for the john value.

Flexibility: The doo factory constructor allows you to pass in a dynamic value, thus solving the initial problem.

Example Usage

Here’s how you can use the TestEnum class:

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Benefits of This Approach

You retain the intuitive naming of enum-like values.

You gain the flexibility of using dynamic values without encountering compilation errors.

It aligns well with Dart's type safety and design principles.

Conclusion

While Dart’s enhanced enums are limited when it comes to non-constant values, using classes provides an effective workaround. This approach allows you to maintain clear and organized code while utilizing dynamic values in your applications. Don't let enums hold you back—embrace the class option for greater flexibility in your Dart projects!