Commit 1a83adfe authored by Alexander Hirsch's avatar Alexander Hirsch

Add person_id example

parent 7f875dd6
CXXFLAGS = -std=c++17 -Wall -Wextra -O2
OUT = person_id
all: $(OUT)
$(RM) $(OUT)
.PHONY: all clean
// This example illustrates the use of IDs for referencing objects. IDs serve as
// a viable alternative to smart pointers, raw pointers, and values.
// The focus of this example lies on a clean and straight forward interface
// *and* implementation.
#include <algorithm>
#include <iostream>
#include <memory>
#include <string>
#include <vector>
// Person itself is just an ID.
using Person = int;
// Renaming the original struct to PersonData is a sensible change.
struct PersonData {
std::string firstName;
std::string lastName;
int age;
// This database generates Person IDs and stores the corresponding PersonData.
class PersonDatabase {
Person createPerson(const PersonData &personData)
return m_personData.size() - 1;
const PersonData &getPersonData(Person person) const { return; }
// A simple vector will do, the resulting Person ID is simply the index of
// the corresponding PersonData. This enables fast lookups.
std::vector<PersonData> m_personData;
class Room {
Room(int id, size_t capacity) : m_id(id), m_capacity(capacity) {}
bool enter(Person person)
if (m_peopleInside.size() >= m_capacity) {
return false;
return true;
void exit(Person person)
const auto it = std::find(m_peopleInside.begin(), m_peopleInside.end(), person);
if (it != m_peopleInside.end()) {
const std::vector<Person> &peopleInside() const { return m_peopleInside; }
int m_id;
size_t m_capacity;
std::vector<Person> m_peopleInside;
int main()
PersonDatabase database;
const auto mike = database.createPerson({"Mike", "Smith", 24});
const auto jane = database.createPerson({"Jane", "Saw", 28});
Room room{128, 42};
for (auto person : room.peopleInside()) {
std::cout << "Hallo " << database.getPersonData(person).firstName << "\n";
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