Ticket #12542: main.cpp

#include "boost/multi_index_container.hpp"
#include "boost/multi_index/member.hpp"
#include "boost/multi_index/ordered_index.hpp"
#include <boost/multi_index/sequenced_index.hpp>

#include <algorithm>
#include <list>
#include <iostream>

using namespace boost::multi_index;

struct employee
{
    int id;
    std:: string name;
    employee(int id, std::string const& name): id{id}, name{name}{}
};

bool operator<(employee const& lhs, employee const& rhs)
{
    return lhs.id < rhs.id;
}

std::ostream& operator<<(std::ostream& os, employee const& e)
{
    os << e.name << " [" << e.id << "]"; return os;
}


struct id;
struct name;

// define a multiply indexed set with indices by id and name
using employees = boost::multi_index_container<
        employee,
        indexed_by<
                // sort by operator<(employee, employee)
        ordered_unique<tag<id>, identity<employee>>,
                // sort by less<string> on name
        ordered_non_unique<tag<name>, member<employee, std::string, &employee::name>>>>;

void print_out_by_name(employees const& es)
{
    // get a view to index #1 (name)
    auto & name_index(es.get<name>());
    // use name_index as a regular std::set
    std::copy(
            name_index.begin(),name_index.end(),
            std::ostream_iterator<employee>(std::cout, "\n"));
}


int main()
{
    employees es;
    es.insert({0, "Adam"});
    es.insert({1, "Eve"});
    es.insert({2, "Bob"});

    std::cout << "Employee ids must be unique.\n";
    std::cout << "Here are the original records:\n";
    print_out_by_name(es);

    std::cout << "Changing Bob's id to one which is already taken (1).\n";
    std::cout << "Calling modify() with a callable that violates the index constraint\n";
    std::cout << "and a rollback callable that does nothing to fix the problem.\n";
    auto& name_index(es.get<name>());
    auto it(name_index.find("Bob"));
    bool succeed{name_index.modify(
            it,
            [](employee& e) {e.id = 1;},
            [](employee& e) { std::cout << "[confirming rollback called]\n";})};
    std::cout << "Call succeeded: " << std::boolalpha << succeed << "\n";
    std::cout << "Here are the post-modify-call records.\n";
    print_out_by_name(es);
    std::cout << "We now have a duplicated unique key value.\n";

    std::cout << "\nIf the rollback fails to correct the problem, should the record not be deleted?\n";
}