std::atomic_flag::operator= (3) Linux Manual Page

std::atomic_flag::operator= – std::atomic_flag::operator=

Synopsis

Defined in header<atomic>

    atomic_flag &operator=(const atomic_flag &) = delete;
(1)(since C++ 11)

    atomic_flag &
    operator=(const atomic_flag &) volatile = delete;
(2)(since C++ 11)

std::atomic_flag is not assignable, its assignment operators are deleted.