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Defining fmt::Display and fmt::Debug Together in Rust

Learn how to implement both `fmt::Display` and `fmt::Debug` for your Rust structures efficiently, including when to share implementations and best practices. --- This video is based on the question https://stackoverflow.com/q/69964338/ asked by the user 'Phil-ZXX' ( https://stackoverflow.com/u/2287458/ ) and on the answer https://stackoverflow.com/a/69965338/ provided by the user 'Kevin Reid' ( https://stackoverflow.com/u/99692/ ) 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: Define fmt::Display and fmt::Debug together 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 fmt::Display and fmt::Debug in Rust In Rust programming, you might encounter situations where you need to output your custom types to the console or during debugging. The traits fmt::Display and fmt::Debug serve these purposes, but they have slightly different goals. This guide will explore how to define both traits for your custom structures in a clean and efficient manner using Rust's formatting capabilities. The Problem: Can You Define Both Traits Together? A common question among Rust developers, especially for those just starting out, is whether it's possible to implement both fmt::Display and fmt::Debug for a single structure using the same code. For instance, when you write unit tests or use print statements, having both traits can ensure your code is both functional and user-friendly. Let's consider the following example using a struct called MyDate: [[See Video to Reveal this Text or Code Snippet]] In this code, you are likely trying to achieve two goals: printing the MyDate struct for user-friendly outputs and using assertions for testing that require a detailed view. The Question Formulated The original question arises: is there a way to create a single implementation of your fmt methods, so as to avoid duplication? Specifically, is there a syntax like impl fmt::Debug, fmt::Display for MyDate { ... } that could simplify your work? Or is it common practice to simply use -[derive(Debug)] at the top of your struct? The Solution: Implementing Both Traits Efficiently Can You Combine Implementations? In most scenarios, the outputs for Display and Debug differ because they serve different purposes: fmt::Display: Intended for end-users, with a polished and user-friendly output. fmt::Debug: Used for debugging with a more detailed, unambiguous output that includes all fields of the struct. However, when the formatting of both is similar, as in the MyDate example where it’s straightforward and clear, you can reuse the Display implementation in Debug. This, as shown in the example code, can be done using a simple call to self in fmt::Debug, which utilizes the fmt method from fmt::Display. This effectively enables you to share the logic while also maintaining the semantic clarity that each trait provides. Making the Choice: Manually Implement vs. Deriving While manually implementing both traits gives you control over formatting: If the formatting requirement doesn't differ significantly, you can certainly consider deriving Debug alongside other traits for cleaner code. For instance, you can use -[derive(Debug)] at the top of your struct. Additional Best Practices For best practices when implementing traits in Rust, consider the following: Maintain Clarity: Ensure that your Debug output is comprehensive and unambiguous. It should represent the full state of the struct. Use Derives When Possible: If suitable, leverage the -[derive(PartialEq)] for equality checks to avoid pitfalls associated with manual implementations. This also reduces the chance of errors if you modify the struct by forgetting to add a new field to your equality comparison. Conclusion In conclusion, while it's possible to implement fmt::Display and fmt::Debug together, choosing when and how to do so depends on your struct's requirements. If you have similar formatting for both traits, reusing the same implementation is both efficient and effective. Otherwise, leveraging Rust's powerful deriving capabilities can keep your code clean and maintainable. By keeping these principles in mind, you can ensure your Rust applications are well-structured and your custom types are both user-friendly and debug-friendly.