Скачать или смотреть Understanding Immutable Classes with Calculated Fields in Dart

Explore how to create `immutable` classes in Dart with calculated fields using factory constructors, ensuring constant evaluation rules are adhered to.
---
This video is based on the question https://stackoverflow.com/q/73454902/ asked by the user 'Jan Tosovsky' ( https://stackoverflow.com/u/2523836/ ) and on the answer https://stackoverflow.com/a/73459348/ provided by the user 'lrn' ( https://stackoverflow.com/u/2156621/ ) 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: Immutable classes with calculated fields

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.
---
Understanding Immutable Classes with Calculated Fields in Dart

In the world of Dart programming, immutability plays a significant role in creating robust and error-free applications. However, sometimes you face challenges when needing to initialize immutable fields with calculated values that cannot be directly derived in the initializer list. If you've ever wondered how to achieve this while adhering to Dart's immutability rules, you've landed in the right place!

The Challenge of Immutability with Calculated Fields

The Problem

As developers, we often encounter a situation where we want to create an immutable class but need to perform calculations to initialize its fields. For instance, consider a scenario where you're trying to create a class that represents a circle. Specifically, if you want to initialize a Circle object with three points instead of defining it by a center and a radius, the standard constructor might not suffice.

Why the Standard Approach Might Fail

In Dart, when you define fields as final, these must be initialized at the point of declaration or within the constructor. However, the logic needed to compute values often doesn't allow for this kind of initialization. This is especially true if the calculations are not simple or involve non-constant expressions.

An Effective Solution: The Factory Constructor

Using Factory Constructors

Factory constructors in Dart allow you to define alternative ways to construct instances of a class. This is particularly helpful when dealing with complex initialization logic. Here's how you can use a factory constructor to initialize a circle using three points:

Circle Class Example

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

Explanation of the Code

Final Fields: The Circle class has two final fields: center and radius.

Factory Constructor: The Circle.fromPoints factory constructor takes three Point objects and calculates the center and radius, returning a new Circle instance.

Immutable Result: Even though the Circle is initialized with calculated values, it remains immutable as its fields are marked as final.

Key Takeaway

Using a factory constructor allows you to break the constraints of constant expression evaluation. In the provided example, you can initialize the Circle object correctly without falling into issues related to immutability.

Important Note: While using the const keyword, ensure that you're not violating constant evaluation rules. Only use const where necessary, especially when non-constant values are involved.

Conclusion

Creating immutable classes with calculated fields in Dart is indeed achievable through the thoughtful use of factory constructors. While you can leverage Dart’s immutability contracts effectively, always keep an eye on constant evaluation constraints. Embrace the challenge of designing your applications to maintain data integrity while achieving your software project goals seamlessly!

With this understanding, you’re now equipped to handle immutability in Dart with calculated fields confidently.