Labeled Tuples (Informed Position)

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Adds labels to tuple fields, implemented as an optional label on every field and landed in Jane Street’s OCaml branch, with a small compiler change (no row polymorphism). Patterns support partial extraction and reordering only when the compiler knows the tuple type. Labels incur no runtime cost unlike polymorphic-variant or object hacks. Duplicate and omitted labels are allowed; projection is not added yet. The feature proves popular and is used in thousands of files across the codebase.

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" chapters (21)

1. 0:00Introduction
2. 1:19Labeled tuples in OCaml
3. 2:42Label syntax and types
4. 3:24Partial pattern matching
5. 4:26Optional and repeated labels
6. 5:49Adding label tuples
7. 7:12Code without label tuples
8. 9:16Alternatives to labels
9. 11:21Design and implementation
10. 13:24Popularity of labels
11. 14:06Comparison with SML Flex records
12. 15:29Labels vs records
13. 16:12History of Flex records
14. 17:15Future extensions
15. 19:10Q&A: Design and optional params
16. 20:13Q&A: Recursive types
17. 20:54Q&A: Repeated labels issue
18. 21:37Q&A: Scala’s similar feature
19. 22:22Q&A: No Labels flag
20. 22:44Q&A: Pattern matching order
21. 23:48Q&A: Runtime efficiency