60: Advanced Conversions

This is where I get into the plethora of constructors you need in modern C++ code...or just don't use them and go with simpler designated initializers until you do.

The Code

This code may need to be demonstrated more interactively to show each of the constructors used and why. Could be a really large exercise.

View Source file ex60.cpp Only

#include <fmt/core.h>
#include <chrono>
#include <thread>
#include <string>
#include <utility>
#include <ranges>

constexpr const int MAX_NAME=1024 * 10;

struct InsanePerson {
  char* name;

  public:

  explicit InsanePerson(const char* s = "") : name(nullptr)
  {
    if(s) {
      name = new char[MAX_NAME];
      std::strcpy(name, s);
    }
  }

  ~InsanePerson() {
    fmt::println("destroy runs! {:p}", name);
    delete[] name;
  }

  // copy
  InsanePerson(const InsanePerson& other)
    : InsanePerson(other.name) {}

  // move
  InsanePerson(InsanePerson&& other) noexcept
    : name(std::exchange(other.name, nullptr)) {}

  // copy assign
  InsanePerson& operator=(const InsanePerson& other) {
    return *this = InsanePerson(other);
  }

  // move assign
  InsanePerson& operator=(InsanePerson&& other) noexcept
  {
    std::swap(name, other.name);
    return *this;
  }


  void print() {
    fmt::println("I am {}.", name);
  }
};

int main(int argc, char* argv[]) {
  std::vector<InsanePerson> others;
  std::array<InsanePerson, 20> people;

  fmt::println("---- setup loop");
  for(size_t i = 0; i < 10; i++) {
    InsanePerson who("Test");
    // trigger copy
    others.push_back(who);
    fmt::println("name after copy: {:p}", who.name);

    // trigger move
    others.emplace_back(std::move(who));
    fmt::println("name after move: {:p}", who.name);
  }

  fmt::println("--- enumerate badness");
  for(auto [i, who] : std::views::enumerate(others)) {
    fmt::println("before move: {:p}", who.name);
    // trigger copy assign and move assign
    people[i] = who;
    fmt::println("after  move: {:p}", who.name);
  }

  fmt::println("--- print everyone");
  for(auto& who : people) {
    who.print();
  }

  fmt::println("!!!!!!!!!!! end");
}

The Breakdown

line of code

Description.

The Discussion

Blah blah.

Further Study

• https://en.cppreference.com/cpp/language/rule_of_three
• https://en.cppreference.com/cpp/language/move_assignment
• rvalue reference https://en.cppreference.com/cpp/language/reference
• forwarding reference (so different! lol) https://en.cppreference.com/cpp/utility/forward
• https://en.cppreference.com/cpp/language/value_category