How to break an ABI and keep your users happy

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" summary

Google had long used a custom global string implementation (copy‑on‑write vs SSO) that costs about 2% slowdown and becomes unmanageable across a growing codebase (from ~1M to 150M LOC over the years). The team auto‑refactors sources (half a year) and builds the standard library twice with different inline namespaces, producing a fat standard library that contains both ABIs so old prebuilt binaries keep working; it succeeds at compatibility but doubles library size and is acknowledged as a suboptimal, temporary fix.

AI-written summary · about

" chapters (35)

1. 0:00Introduction to the topic
2. 1:33History of string classes
3. 2:51Copy-on-write limitations
4. 3:55Small string optimization
5. 5:04Inline namespaces explained
6. 6:16Understanding ABI vs API
7. 7:15Google C++ history
8. 8:23The COW string problem
9. 9:45Moving to standard libraries
10. 10:33The impostor string solution
11. 11:47Lessons from the impostor
12. 12:48Dependencies and performance
13. 14:05The hidden string piece
14. 15:32Fixing the global namespace
15. 16:25Open sourcing common libraries
16. 17:37Replacing standard string
17. 18:51Serving two masters
18. 20:14The technical solution
19. 21:53Lessons in design
20. 22:52Mistakes are inevitable
21. 23:42Fail faster
22. 24:37Design for change
23. 25:29API contracts
24. 26:26Avoiding forward declaration
25. 27:40Defining behavior
26. 28:35Function contracts
27. 29:43ABI and memory layout
28. 30:58ABI and virtual tables
29. 32:19Calling conventions
30. 33:02Mangled names
31. 34:22Innocent changes
32. 35:10Summary of ABI stability
33. 35:45Binary break preparation
34. 37:06Pimpl idiom
35. 37:45Q&A and conclusion

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