Stories with Tag Value Objects

• How to create value objects in Ruby – the idiomatic way

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  Posted: 2025-03-21 09:43:16

  Verbose tl;dr

  This post advocates for using Ruby's built-in features like Struct and immutable data structures (via freeze) to create simple, efficient value objects. It argues against using more complex approaches like dry-struct or Virtus for basic cases, highlighting that the lightweight, idiomatic approach often provides sufficient functionality with minimal overhead. The article illustrates how Struct provides concise syntax for defining attributes and automatic equality and hashing based on those attributes, fulfilling the core requirements of value objects. Finally, it demonstrates how to enforce immutability by freezing instances, ensuring predictable behavior and preventing unintended side effects.

  This blog post elucidates the creation of value objects in Ruby, emphasizing the idiomatic approach favored by experienced Ruby developers. It begins by defining what constitutes a value object: an immutable object whose identity is determined solely by its attributes. This means two value objects with the same attribute values are considered equal, regardless of their memory location. The author contrasts this with entity objects, which maintain individual identities even with identical attribute values.

  The post then delves into the preferred Ruby method for crafting value objects, leveraging the Struct class. Struct provides a concise and efficient mechanism for defining immutable data structures with automatically generated accessor methods. The author demonstrates how to create a simple Point value object using Struct, highlighting the automatic inclusion of methods like #== and #hash which correctly compare objects based on attribute values, fulfilling the core requirements of a value object.

  Furthermore, the post showcases how to incorporate custom methods within Struct-based value objects. This extends their functionality beyond mere data storage. The author uses an example of adding a distance method to the Point object, demonstrating how to encapsulate relevant logic within the value object itself. This exemplifies the power of Struct to create not just data containers, but genuinely useful and self-contained objects.

  The author stresses the importance of immutability for value objects and demonstrates how to enforce it using the #freeze method. Freezing a Struct object prevents any subsequent modification of its attributes, ensuring that its state remains constant throughout its lifecycle, reinforcing its value object nature. The post specifically warns against using OpenStruct for value objects due to its inherent mutability.

  Finally, the post briefly touches upon alternative approaches for creating value objects, including using classes and defining methods manually. However, it reiterates the advantages of the Struct-based approach, highlighting its conciseness, readability, and automatic generation of crucial comparison methods, concluding that Struct is the most idiomatic and therefore preferred way to implement value objects in Ruby. This conciseness minimizes boilerplate code and promotes clarity, aligning with the Ruby philosophy of elegant and expressive code. The post ultimately champions the Struct class as the most effective and Ruby-like solution for creating value objects.

  • ruby
  • Value Objects
  • value types
  • immutable objects
  • programming
  • Software Development
  • object-oriented programming
  • Idiomatic Ruby
  • best practices
  • Coding Style
  • data structures

  Summary of Comments ( 1 )
  https://news.ycombinator.com/item?id=43433648

  Verbose tl;dr

  HN users largely criticized the article for misusing or misunderstanding the term "Value Object." Commenters pointed out that true Value Objects are immutable and compared by value, not identity. They argued that the article's examples, particularly using mutable hashes and relying on equal?, were not representative of Value Objects and promoted bad practices. Several users suggested alternative approaches like using Struct or creating immutable classes with custom equality methods. The discussion also touched on the performance implications of immutable objects in Ruby and the nuances of defining equality for more complex objects. Some commenters felt the title was misleading, promoting a non-idiomatic approach.

  The Hacker News post titled "How to create value objects in Ruby – the idiomatic way" (linking to an article about creating value objects in Ruby) has several comments discussing various aspects of value objects, their implementation in Ruby, and alternative approaches.

  One commenter points out the inherent tension between true value object semantics (immutable, compared by value) and the performance implications of creating new objects for every modification. They highlight the practical compromise often made in Ruby where objects are treated as if they were value objects, even if they are technically mutable under the hood. This commenter also raises the question of whether the performance cost of true immutability is actually significant in typical Ruby applications.

  Another commenter emphasizes the importance of clearly defining equality (==) and hash code (hash) methods when working with value objects in Ruby. They mention that using Struct can simplify this process, but caution against overlooking these crucial methods for correct value object behavior.

  The discussion then delves into specific aspects of Ruby's object model and how it affects value object implementation. One commenter argues against using dup for creating modified copies of value objects, preferring explicit constructor calls or factory methods for clarity and control. They also advocate for defining methods that return new instances rather than modifying the existing object in place. Another commenter suggests leveraging the dry-struct gem, which provides built-in support for immutability and value comparisons. This suggestion sparks a brief comparison of dry-struct with Value and Data.define, two other Ruby gems designed for creating value objects, highlighting the tradeoffs between different approaches.

  A separate thread within the comments discusses the use of freeze for enforcing immutability in Ruby. One commenter cautions against overusing freeze, particularly when dealing with nested data structures. They explain that freeze only provides shallow immutability, leaving deeper layers potentially mutable, which can lead to unexpected behavior.

  Finally, a few comments touch on the broader context of value objects and their relationship to domain-driven design (DDD). They suggest that focusing on the conceptual aspects of value objects, namely their role in representing domain concepts, is more important than the specific implementation details. One commenter highlights the importance of understanding the business logic and how value objects contribute to the overall domain model.

• How to create value objects in Ruby – the idiomatic way

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  Posted: 2025-03-20 10:03:17

  Verbose tl;dr

  This post advocates for using Ruby's built-in features, specifically Struct, to create value objects. It argues against using gems like Virtus or hand-rolling complex classes, emphasizing simplicity and performance. The author demonstrates how Struct provides concise syntax for defining immutable attributes, automatic equality comparisons based on attribute values, and a convenient way to represent data structures focused on holding values rather than behavior. This approach aligns with Ruby's philosophy of minimizing boilerplate and leveraging existing tools for common patterns. By using Struct, developers can create lightweight, efficient value objects without sacrificing readability or conciseness.

  This blog post by Allaboutcoding details the preferred, or idiomatic, method for creating Value Objects within the Ruby programming language. It begins by defining Value Objects, explaining that they represent concepts based on their data, not their identity. Two Value Objects with the same data are considered equal, regardless of whether they are the same instance in memory. This contrasts with Entities, which are defined by their identity. The post uses the example of a Money object: $5 is $5, regardless of the specific bills or coins representing it.

  The article then outlines the traditional approach for creating Value Objects in Ruby, which involves overriding the == method to compare attributes. This approach, while functional, can become cumbersome when multiple attributes are involved, leading to repetitive and potentially error-prone code.

  The post then introduces the recommended idiomatic approach using the Struct class. Struct provides a concise way to define classes with predefined accessor methods for the specified attributes. By inheriting from Struct, one can easily create a Value Object with automatic attribute readers and a built-in implementation of equality based on attribute values. This significantly simplifies the creation of Value Objects and reduces the amount of boilerplate code required.

  The post demonstrates this with the Money example, showing how a Money Value Object can be concisely defined using Struct.new(:amount, :currency). It further explains that this method inherently provides the desired equality comparison based on the amount and currency attributes.

  The author then highlights the advantages of using Struct for Value Objects. These include improved code readability and maintainability due to its brevity, automatic generation of accessor methods, and the built-in, correct implementation of equality comparison, which eliminates the need for manual overriding of the == method and reduces the risk of introducing errors.

  Finally, the post concludes by reiterating that the use of Struct is the recommended and idiomatic way to create Value Objects in Ruby, encouraging readers to adopt this approach for its conciseness and built-in functionalities that perfectly align with the requirements of Value Objects. It emphasizes that this method simplifies the process and makes the code easier to understand and maintain.

  • ruby
  • Value Objects
  • object-oriented programming
  • Idiomatic Ruby
  • Ruby Best Practices
  • Software Development
  • programming
  • data modeling
  • Domain Modeling
  • Immutability
  • data integrity
  • code quality
  • refactoring

  Summary of Comments ( 2 )
  https://news.ycombinator.com/item?id=43421324

  Verbose tl;dr

  HN commenters largely criticized the article for misusing or misunderstanding the term "value object." They argued that true value objects are defined by their attributes and compared by value, not identity, using examples like 5 == 5 even if they are different instances of the integer 5. They pointed out that the author's use of Comparable and overriding == based on specific attributes leaned more towards a Data Transfer Object (DTO) or a record. Some questioned the practical value of the approach presented, suggesting simpler alternatives like using structs or plain Ruby objects with attribute readers. A few commenters offered different ways to implement proper value objects in Ruby, including using the Values gem and leveraging immutable data structures.

  The Hacker News post titled "How to create value objects in Ruby – the idiomatic way" has generated several comments discussing various aspects of value objects in Ruby and alternative approaches.

  One commenter points out that using Struct for value objects can be problematic when dealing with inheritance, particularly when attributes are added to subclasses. They suggest using Data.define as a potential solution to this issue, as it creates immutable objects by default. This commenter also mentions that the Comparable module provides a more concise way to define equality and comparison methods based on the value object's attributes. They provide a code example illustrating this approach.

  Another commenter questions the necessity of the article's approach, suggesting that a simple class with an initialize method and attribute readers would suffice in many cases. They argue against over-engineering simple value objects, emphasizing the importance of readability and maintainability. This commenter also raises the potential for performance implications when using modules like Comparable, suggesting benchmarking to determine the actual impact.

  A different user focuses on the use of ::new in the original article's example, explaining that it's not required and is likely a stylistic choice. They point out that using just .new would be the more common and concise approach in Ruby.

  The conversation then shifts towards a discussion of the benefits and drawbacks of using Struct versus defining a custom class. One commenter highlights that Struct can be handy for quick prototyping or when the value object is extremely simple. However, they acknowledge the limitations of Struct, such as difficulties with inheritance and the inability to easily add custom methods. Another commenter mentions using OpenStruct as an alternative, but acknowledges its own set of trade-offs, particularly regarding performance.

  Finally, a commenter draws attention to the dry-struct gem from the dry-rb ecosystem, advocating for its use in creating more robust and feature-rich value objects. They specifically mention the gem's ability to handle type coercion and validation, making it a suitable option for more complex scenarios. Another comment chimes in endorsing dry-struct and adding that using it is generally superior to relying on Struct. They mention dry-struct's ability to specify types, which aids in catching errors early.