std::initializer_list::size
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                    < cpp | utility | initializer list
                    
                                                            
                    | size_type size() const; | (since C++11) (until C++14) | |
| constexpr size_type size() const; | (since C++14) | |
Returns the number of elements in the initializer list, i.e. std::distance(begin(), end()).
Parameters
(none)
Return value
the number of elements in the initializer list
Exceptions
noexcept specification:  
noexcept
  Complexity
Constant