feat: implement xsd:double codec

[mark-dropbear]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @mark-dropbear, 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 introduces comprehensive support for the xsd:double data type, a fundamental addition that expands the library's capability to accurately process and represent XML Schema Definition floating-point numbers. By implementing a dedicated codec, the library can now seamlessly convert between XSD string formats and Dart's native double type, including special values like infinity and NaN, and correctly handle scientific notation.

Highlights

• New xsd:double Codec: Implemented a new codec (XsdDoubleCodec) to handle the xsd:double XML Schema Definition data type, allowing for conversion between XSD string representations and Dart's double type.
• Special Value Handling: The xsd:double codec correctly handles special floating-point values such as NaN (Not a Number), INF (Positive Infinity), and -INF (Negative Infinity) during both encoding and decoding.
• Scientific Notation Support: The decoder now correctly parses scientific notation (e.g., 1.2E3, 1.2e3) for xsd:double values, and the encoder converts Dart's double string representation to uppercase 'E' for scientific notation to match XSD canonical form.
• Documentation and Tests: Updated the CHANGELOG.md and README.md to reflect the new xsd:double support, and added comprehensive unit tests to ensure the correctness of the codec's encoding and decoding logic.

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 implements the xsd:double codec and its corresponding encoder and decoder. The implementation correctly handles special values like INF, -INF, and NaN, and applies the collapse whitespace rule as per the XSD specification. The code is clean and follows the existing structure. My feedback focuses on enhancing the test suite to cover more edge cases, such as scientific notation encoding, whitespace handling during decoding, and invalid input validation, to ensure the codec is robust.