Make all Literals default-constructible; fixes #536

[liuzicheng1987]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @liuzicheng1987, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the flexibility of the rfl::Literal type by ensuring all instances can be default-constructed, addressing a prior limitation. Concurrently, a new test has been introduced to verify the correct handling of std::chrono::seconds with default-if-missing behavior during JSON serialization and deserialization, improving the robustness of the library's type handling.

Highlights

• Literal Default Construction: The rfl::Literal class has been updated to make its default constructor universally available, removing the previous restriction that only allowed single-field literals to be default-constructible. This change simplifies the usage of Literal objects by allowing them to be default-initialized regardless of their field count.
• New Test Case: A new test file test_duration_default.cpp has been added to validate the serialization and deserialization of std::chrono::seconds within a struct, specifically when using rfl::DefaultIfMissing with rfl::json.

Using Gemini Code Assist

The full guide for Gemini Code Assist can be found on our documentation page, here are some quick tips.

Invoking Gemini

You can request assistance from Gemini at any point by creating a comment using either /gemini <command> or @gemini-code-assist <command>. Below is a summary of the supported commands on the current page.

Feature	Command	Description
Code Review	/gemini review	Performs a code review for the current pull request in its current state.
Pull Request Summary	/gemini summary	Provides a summary of the current pull request in its current state.
Comment	@gemini-code-assist	Responds in comments when explicitly tagged, both in pull request comments and review comments.
Help	/gemini help	Displays a list of available commands.

Customization

To customize Gemini Code Assist for GitHub experience, repository maintainers can create a configuration file and/or provide a custom code review style guide (such as PEP-8 for Python) by creating and adding files to a .gemini/ folder in the base of the repository. Detailed instructions can be found here.

Limitations & Feedback

Gemini Code Assist may make mistakes. Please leave feedback on any instances where its feedback is incorrect or counter productive. You can react with 👍 and 👎 on @gemini-code-assist comments. If you're interested in giving your feedback about your experience with Gemini Code Assist for Github and other Google products, sign up here.

You can also get AI-powered code generation, chat, as well as code reviews directly in the IDE at no cost with the Gemini Code Assist IDE Extension.

Footnotes

1. Review the Privacy Notices, Generative AI Prohibited Use Policy, Terms of Service, and learn how to configure Gemini Code Assist in GitHub here. Gemini can make mistakes, so double check it and use code with caution. ↩

[gemini-code-assist]

Code Review

This pull request makes rfl::Literal default-constructible, which is a necessary change to allow features like rfl::DefaultIfMissing to work with types that internally use rfl::Literal, such as std::chrono::duration. The change in include/rfl/Literal.hpp is correct and achieves this goal effectively. I've added one comment to suggest an improvement for the new test case to more thoroughly verify the intended behavior.