In his presentation at RubyKaigi 2023, Richard Huang discusses the concept of "Find and Replace Code Based on AST" (Abstract Syntax Tree) and its relevance in modern coding practices. The AST is a critical data structure that allows programmers to understand and manipulate code more effectively, representing the code as a tree of nodes where each node symbolizes a distinct code structure, such as method definitions or class declarations.

Key points discussed include:
- Definition and Importance of AST: Richard explains how AST is structured, illustrating with an example of a class in Ruby. The AST provides structured representation, making it easier to search and replace code precisely compared to traditional text-based methods.
- Benefits of AST-based Tools: He highlights the advantages of using AST for finding and replacing code, allowing for more accurate searches. For instance, distinguishing between different usages of the same term in code and avoiding false positives in string representations.
- Available Tools: Richard mentions various AST-based tools available within the Ruby ecosystem, such as Rigid and Robocop, as well as his own tool, Synvert, which he created for upgrading Rails projects. Synvert simplifies the process by automating syntax changes during version upgrades.
- Synvert Architecture and Functionality: Synvert uses a domain-specific language (DSL) for defining transformations. Richard demonstrates how Synvert allows users to perform complex queries and mutations of the code’s AST, along with providing tools that cater to both seasoned and novice developers.
- Real-world Applications: He provides examples of how users can execute queries to locate specific structures in the code, like searching for hash rocket keys or identifying setup methods that do not call a super method. He explains how quick updates can be accomplished through Synvert's user-friendly interface.
- Interactive Features and Community Feedback: Richard shares insights about the GUI application for Synvert, enhancing usability for developers by allowing them to review, accept, or reject changes before applying them to their code base. He invites feedback and contributions from the community to continually improve Synvert.

Conclusions and Takeaways: Richard emphasizes the importance of leveraging AST for code manipulation, the power of Synvert, and its user-friendly features which can accelerate development and streamline code upgrades over traditional methods. This presentation serves as a guide for developers looking to enhance their code maintenance practices using AST-based tools.