lib/email.hpp

The following code example is taken from the book
C++ Move Semantics - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2020
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

// raw code

#include <iostream>
#include <cassert>
#include <string>

// class for email addresses
// - asserts that each email address has a @
// - except when in a moved-from state
class Email {
private:
  std::string value;       // email address
  bool movedFrom{false};   // special moved-from state
public:
  Email(const std::string& val)
   : value{val} {
      assert(value.find('@') != std::string::npos);
  }
  Email(const char* val)   // enable implicit conversions for string literals
   : Email{std::string(val)} {
  }

  std::string getValue() const {
      assert(!movedFrom);  // or throw
      return value;
  }
  //...

  // implement move operations to signal a moved-from state:
  Email(Email&& e) noexcept
   : value{std::move(e.value)}, movedFrom{e.movedFrom} {
      e.movedFrom = true;
  }
  Email& operator=(Email&& e) noexcept {
      value = std::move(e.value);
      movedFrom = e.movedFrom;
      e.movedFrom = true;
      return *this;
  }
  // enable copying:
  Email(const Email&) = default;
  Email& operator=(const Email&) = default;
  
  // print out the current state (even if it is a moved-from state):
  friend std::ostream& operator<< (std::ostream& strm, const Email& e) {
    return strm << (e.movedFrom ? "MOVED-FROM" : e.value);
  }
};