The Object Upside Down

on YouTube ↗05m

" summary

Creates an instance of a non-default-constructible type by placing two layout-compatible wrapper structs into a union, activating one, reading the other through their common initial sequence, reinterpret_casting that member to the wrapper type and then to the target base to yield a T without calling any constructors. Relies on standard-layout and an inactive union read* hack that works under current rules but is unsafe; C++20 makes stateless lambdas default-constructible so the workaround becomes unnecessary.

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