std::atomic_flag::operator=
From Cppreference
< cpp | atomic | atomic flag
				
																
				
				
								
				|   Defined in header <atomic>
  
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|   atomic_flag& operator=( const atomic_flag& ) = delete; 
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(1) | (since C++11) | 
|   atomic_flag& operator=( const atomic_flag& ) volatile = delete; 
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(2) | (since C++11) | 
std::atomic_flag is not assignable, its assignment operators are deleted.