Casey Muratori on designing libraries well
Audio Brief
Show transcript
This episode covers Casey Muratori's controversial perspective on effective library design, prioritizing commercial success and practical user needs over common abstract principles.
There are three key takeaways. First, effective library design advice comes from those who have successfully sold libraries in competitive markets. Second, design should prioritize user efficiency by exposing stable data structures, not hiding functionality with restrictive object-oriented principles. Third, a good library's value lies in providing reliable, fundamental building blocks that users can trust.
Muratori asserts that valid library design is proven through commercial success in competitive markets. This experience provides crucial real-world lessons, filtering out impractical or academic approaches.
He criticizes common Object-Oriented Programming principles like data hiding, arguing they are often impractical for users. Users primarily seek to save time or lack the expertise to modify complex internals, making designs that force more code or source modifications counterproductive.
Instead, a good library provides stable, well-defined, and accessible building blocks. The designer's role is to identify and guarantee the stability of these core components, exposing them directly for maximum user control and flexibility.
Ultimately, this approach advocates for a practical, commercially-tested philosophy where library value is measured by its utility and reliability to the end user.
Episode Overview
- Casey Muratori asserts that valid library design advice only comes from those who have successfully sold a library in a competitive market, as this experience provides crucial, real-world lessons.
- He criticizes common Object-Oriented Programming (OOP) principles like data hiding, arguing they are often impractical for library users who want to either save time or lack the expertise to modify complex internals.
- Muratori uses the evolution of the "Granny 3D" animation library to contrast a failed, abstract approach with a successful one that exposed its core data structures directly to the user.
- The discussion highlights that a good library provides stable, well-defined, and accessible building blocks, rather than hiding functionality behind restrictive APIs.
Key Concepts
- Commercial Viability as a Metric for Good Design: The central idea is that the ultimate test of a library's design is whether people are willing to pay for it in a competitive market. This proves the design solves real problems effectively.
- Data-Oriented vs. Object-Oriented Library Design: The podcast contrasts the OOP philosophy of hiding data (encapsulation) with a data-oriented approach that exposes core data structures, giving users more direct control and flexibility.
- Understanding the Library User: The speaker emphasizes that people use libraries primarily to save time or because they don't know how to implement the functionality themselves. Therefore, design choices that require users to write more code (like subclassing) or modify source are often counterproductive.
- The "Promise" of an API: A well-designed library's job is not to hide everything, but to figure out which components can be guaranteed to be stable and then "promise" that stability by exposing them as reliable building blocks.
Quotes
- At 00:01 - "You should never take library design advice from anyone who hasn't had to make a living selling a library in a competitive arena." - Muratori establishes his core premise that commercial success is the best filter for good design principles.
- At 03:06 - "Your goal is not to hide everything. It's for you to do the work up front to figure out what you can promise, and then promise that. That is what makes a library good." - This quote summarizes his philosophy that a library designer's job is to provide a stable, predictable foundation for users, not just abstract away the implementation details.
Takeaways
- Prioritize library design advice from practitioners with experience in competitive, commercial environments.
- Design APIs and libraries with the end-user's primary motivations in mind, such as saving time and effort.
- Favor exposing stable, well-defined data structures over forcing all interactions through restrictive function calls.
- A library's value lies in providing reliable, fundamental building blocks that users can trust won't change unexpectedly.
- When a design forces users to modify the library's source code to solve their problem, it may be a sign that the library's abstractions are failing to meet real-world needs.
