CppCoreGuidelines F.50 当不能用函数实现的时候（使用局部变量，写局部函数），使用 lambda

// -*- compile-command: "g++ -std=c++20 code.cpp && ./a"; -*-
#include <iostream>
#include <gsl/gsl>
using namespace std;
using namespace gsl;
// writing a function that should only take an int or a string
// -- overloading is natural
void f(int);
void f(const string&);

// writing a function object that needs to capture local state and appear
// at statement or expression scope -- a lambda is natural
using work = int;
vector<work> lots_of_work() {
    return vector<work>{1,2,3,4,5,6};
}
int main()
{
    vector<work> v = lots_of_work();
    for (int tasknum = 0; tasknum < max; ++tasknum) {
        pool.run([=, &v] {
            /*
              ...
              ... process 1 / max - th of v, the tasknum - th chunk
              ...
            */
        });
    }
    pool.join();
}