On Tuesday, 24 February 2026 at 15:30:39 UTC, H. S. Teoh wrote:
On Tue, Feb 24, 2026 at 03:48:46AM +0000, monkyyy via
Digitalmars-d-learn wrote:
Im going to try doing something with fat structs, what sort of
syntax and api niceitys would big fat-struct advocates say are
nessery?
What's a "fat struct"?
T
In programming, the term "fat struct" (or "fatty struct") refers
to a data structure design philosophy, notably advocated by
programmer Casey Muratori, that prioritizes data locality,
performance, and predictability over object-oriented design
principles like deep inheritance hierarchies. [1, 2]
Core Principles
The fat struct approach represents a fundamental difference in
how software development priorities are ordered, focusing on
efficiency over abstract ideals.
• Packs Related Data: It involves grouping all related data into
a single, contiguous block of memory within one structure, rather
than spreading it across multiple objects that require pointers
and indirection to access.
• Prioritizes Cache Efficiency: By keeping frequently accessed
data physically close in memory, this design makes better use of
modern CPU caches, leading to significant performance
improvements.
• Avoids Unnecessary Abstraction: It eschews complex
object-oriented programming (OOP) patterns, preferring simple
control flow and a design that more directly reflects what the
computer hardware is actually doing.
• Uses Unions Judiciously: While the primary goal is a single
structure, unions might be used to save space if some fields are
mutually exclusive, though this can make debugging more complex.
[2, 3]
Comparison to OOP
The fat struct approach is often contrasted with the traditional
OOP paradigm where specialized classes inherit properties and
methods from a base class.
• Inheritance vs. Type Property: Instead of creating multiple
specialized classes (e.g., and inheriting from ), a single
"fat" struct would contain all possible properties (like and )
and use an explicit field to determine which behaviors and data
are relevant.
• Performance Trade-off: The OOP approach is often seen as more
maintainable and easier to extend, while the fat struct approach
trades some of that perceived maintainability for raw performance.
• Data-Oriented Design: The philosophy is a key component of
data-oriented design (DOD), where the focus is on how data is
laid out in memory and accessed, rather than modeling real-world
entities with class hierarchies. [1, 2, 4, 5]
Practical Implementation Tips
If you are interested in applying these principles, advocates
suggest a pragmatic approach:
1. Start with Data Access Patterns: Design your structures around
how your code actually uses the data, not in an abstract ideal.
2. Measure Performance: The benefits of this approach should be
measurable; benchmark before and after implementation to ensure
the trade-off is worthwhile.
3. Document Layout Decisions: Clearly document the rationale
behind your memory layouts for future maintainers. [6, 7]
[1] https://orangegnome.com/posts/3633/team-fat-posts
[2]
https://levelup.gitconnected.com/fatty-structs-casey-muratoris-approach-to-data-structure-design-ad4753caaf6b
[3] https://www.computerenhance.com/p/q-and-a-80-2025-10-31
[4] https://www.yegor256.com/2020/02/19/fat-skinny-design.html
[5]
https://www.reddit.com/r/roguelikedev/comments/1bv4k7p/any_tutorial_about_dataoriented_programming_for/
[6]
https://levelup.gitconnected.com/fatty-structs-casey-muratoris-approach-to-data-structure-design-ad4753caaf6b
[7]
https://levelup.gitconnected.com/fatty-structs-casey-muratoris-approach-to-data-structure-design-ad4753caaf6b
All the content above was generated by AI, I'm just annexing to
the post to future readers.
Matheus.
