Don't blindly prefer `emplace_back` to `push_back` (2021)(quuxplusone.github.io)

    #include <format>
    #include <string>
    #include <vector>
    
    struct my_type {
      std::string data;
    
      my_type(int value): data(value, 'A') 
      {
        puts("int ctor\n");         
      }
    
      my_type() { puts("default ctor\n"); }
      my_type(const my_type&) { puts("copy ctor\n"); }
      my_type(my_type&&) noexcept { puts("move ctor\n"); }
    
      my_type& operator=(const my_type&) { puts("copy assign\n"); return *this; }
      my_type& operator=(my_type&&) noexcept { puts("move assign\n"); return *this; }
    };
    
    int main()
    {
      puts("Case A\n");
      {
        std::vector<my_type> vec;
        vec.emplace_back(123);
      }
    
      puts("Case B\n");
      {
        std::vector<my_type> vec;
        vec.push_back(my_type{123});
      }
    }
    

    my_type* mem_begin = std::allocator<my_type>::allocate(...); 

    std::construct_at(&mem_begin[0], 123);

    int ctor

    my_type::my_type(int)

    my_data* mem_begin = std::allocator<my_data>::allocate(...); 
    ...
    std::construct_at(&mem_begin[0], instance_of_my_data_passed_in_argument);

    int ctor

    move ctor