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hash<std::unique_ptr> |
template<class T,class Deleter> struct hash<std::unique_ptr<T, Deleter>>; | (since C++11) | |
The template specialization ofstd::hash forstd::unique_ptr<T, Deleter> allows users to obtain hashes of objects of typestd::unique_ptr<T, Deleter>.
The specializationstd::hash<std::unique_ptr<T,D>> is enabled (seestd::hash) ifstd::hash<typenamestd::unique_ptr<T,D>::pointer> is enabled, and is disabled otherwise.
When enabled, for a givenstd::unique_ptr<T, D> p, this specialization ensures thatstd::hash<std::unique_ptr<T, D>>()(p)==std::hash<typenamestd::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.
#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): acac20hash(foo): acac20*up==*foo: true Foo(5)hash(up): acac20hash(other): acbc50*up==*other: true ~Foo()~Foo()
(C++11) | hash function object (class template)[edit] |
