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> int atexit_b(void (^function)(void));
> The atexit_b() function behaves identically to atexit(), except that it takes a block, rather than a function pointer.
なにこれ⁉️
https://man.freebsd.org/cgi/man.cgi?query=atexit&sektion=3&manpath=freebsd-release-ports
これか。clangの拡張カナ？
https://clang.llvm.org/docs/BlockLanguageSpec.html