std::hash<std::unique_ptr>
From cppreference.com
template< class T, class Deleter >
struct hash<std::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.
When enabled, 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 <functional>
#include <iostream>
#include <memory>
struct Foo
{
Foo(int num) : nr(num) { std::cout << "Foo(" << nr << ")\n"; }
~Foo() { std::cout << "~Foo()\n"; }
bool operator==(const Foo &other) const { return nr == other.nr; };
int nr;
};
int main()
{
std::cout << std::boolalpha << std::hex;
Foo* foo = new Foo(5);
std::unique_ptr<Foo> up(foo);
std::cout << "hash(up): " << std::hash<std::unique_ptr<Foo>>()(up) << '\n'
<< "hash(foo): " << std::hash<Foo*>()(foo) << '\n'
<< "*up==*foo: " << (*up == *foo) << "\n\n";
std::unique_ptr<Foo> other = std::make_unique<Foo>(5);
std::cout << "hash(up): " << std::hash<std::unique_ptr<Foo>>()(up) << '\n'
<< "hash(other): " << std::hash<std::unique_ptr<Foo>>()(other) << '\n'
<< "*up==*other: " <<(*up == *other) << "\n\n";
}
Possible output:
Foo(5)
hash(up): acac20
hash(foo): acac20
*up==*foo: true
Foo(5)
hash(up): acac20
hash(other): acbc50
*up==*other: true
~Foo()
~Foo()
See also
(C++11) |
hash function object (class template) |
