std::hash<std::unique_ptr> (3) - Linux Manuals

std::hash<std::unique_ptr>: std::hash<std::unique_ptr>

NAME

std::hash<std::unique_ptr> - std::hash<std::unique_ptr>

Synopsis

template<class T, class Deleter> struct hash<unique_ptr<T, Deleter>>; (since C++11)

The template specialization of std::hash for std::unique_ptr<T, Deleter> allows users to obtain hashes of objects of type std::unique_ptr<T, Deleter>.

The specialization std::hash<std::unique_ptr<T,D>> is enabled (see std::hash) if std::hash<typename std::unique_ptr<T,D>::pointer> is enabled, and is disabled otherwise. (since C++17)

When enabled,
(since C++17) for a given std::unique_ptr<T, D> p, this specialization ensures that std::hash<std::unique_ptr<T, D>>()(p) == std::hash<typename std::unique_ptr<T, D>::pointer>()(p.get()).
The member functions of this specialization are not guaranteed to be noexcept because the pointer may be a fancy pointer and its hash might throw.

Example

// Run this code

  #include <iostream>
  #include <memory>
  #include <functional>

  struct Foo {
      Foo() { std::cout << "Foo...\n"; }
      ~Foo() { std::cout << "~Foo...\n\n"; }
  };

  int main()
  {
      Foo* foo = new Foo();
      std::unique_ptr<Foo> up(foo);

      std::cout << "hash(up): " << std::hash<std::unique_ptr<Foo>>()(up) << '\n';
      std::cout << "hash(foo): " << std::hash<Foo*>()(foo) << '\n';
  }

Output:

  Foo...
  hash(up): 3686401041
  hash(foo): 3686401041
  ~Foo...