std::hash <std::unique_ptr>
From cppreference.com
< cpplrm; | memorylrm; | unique ptr
| 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>.
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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...
See also
| (C++11) |
hash function object (class template) |