In the talk titled "I can't believe it's not an attribute!" presented by Stefan Exner at Ruby Unconf 2019, the speaker explores innovative strategies for managing application-wide settings and user-specific preferences in Ruby on Rails applications.

Stefan begins by reflecting on his long-standing experience with Ruby on Rails, highlighting common challenges in handling various configurations effectively. He emphasizes the need for a streamlined approach to manage settings without cluttering the database or relying heavily on migrations, particularly for temporary features that frequently arise in development.

Key Points Discussed:
- Application-Wide Settings: Exner introduces the concept of using a key-value store, creating an application_settings table to manage dynamic values such as application names or contact emails.
- User-Specific Settings: He discusses the frustration of default settings reverting and proposes a user table with specific fields to store preferences, but acknowledges potential clutter as more settings are added.
- Serialization: The use of the serialize function to store complex objects in one field is presented as a traditional solution, though it lacks elegance and could lead to complexities in handling data structures.
- Setting Accessor: Exner proposes a novel "setting accessor" approach, which allows for a flexible and cleaner method of defining settings attached to specific records while behaving like standard attributes in Active Record. This design facilitates variable management without excessive database alterations.
- Temporary Features: He emphasizes the importance of handling temporary functionalities without creating permanent migrations, which can be cumbersome to manage and revert.
- Caching: Addressing the performance management, Exner invites insights on maintaining coherence when settings require constant reading and proposes lazy loading for efficiency.

Examples: Throughout the presentation, Stefan showcases practical examples of how settings can be defined, retrieved, and modified seamlessly, using familiar Active Record interfaces. For instance, he explains how a user might access and set items per page in their view settings, demonstrating how automatic controller paths are handled in Rails.

Conclusions: Stefan concludes that his setting accessor solution runs efficiently in production, highlighting its flexibility amid Active Record changes over the years while requesting audience contributions for further enhancements in his approach. The talk underscores a balance between maintaining robust settings management alongside adapting to evolving application requirements without burdening the codebase with unnecessary complexity.

The primary takeaways of the presentation emphasize the significance of applying effective strategies to conquer common Rails challenges regarding settings without compromising the integrity and performance of applications.