lst-0025-book.cpp
// https://godbolt.org/z/cE6G1aErs
auto count(vector<int> arg) { return arg.size(); }
// …
vector input{1,2,3}; // vector<int>
vector outputA(input); // copy
vector outputB = input; // also copy, no assignment
cout << count(input) << '\n'; // call by copy-by-value