Taking a Byte Out of C++ - Avoiding Punning by Starting Lifetimes
summary
Claim: C++23 introduces start_lifetime_as to explicitly begin object lifetimes so bytes can back objects without UB from type punning. Shows concrete implementations: memcopy into an aligned byte buffer, a std::like STD bitcast implemented in portable C++20 style, careful use of std::launder, and an expected‑returning API plus Concepts for validation. Applied to a time‑series DB to achieve zero copy page mapping, variable‑length updates, and audited, reusable lifetime‑starting helpers.
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chapters (6)
- 0:00Start
- 5:42No Type Punning
- 10:36C++ Types May Have Invariants
- 12:30Implicit-Lifetime Types (C++20)
- 30:55Ending an Object's Lifetime
- 40:17Summary
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