tmp/tmpifhxol8c/{from.md → to.md}
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| 1 |
+
##### General <a id="util.smartptr.shared.general">[[util.smartptr.shared.general]]</a>
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The `shared_ptr` class template stores a pointer, usually obtained via
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`new`. `shared_ptr` implements semantics of shared ownership; the last
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remaining owner of the pointer is responsible for destroying the object,
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or otherwise releasing the resources associated with the stored pointer.
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A `shared_ptr` is said to be empty if it does not own a pointer.
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``` cpp
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namespace std {
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template<class T> class shared_ptr {
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public:
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using element_type = remove_extent_t<T>;
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using weak_type = weak_ptr<T>;
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// [util.smartptr.shared.const], constructors
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constexpr shared_ptr() noexcept;
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constexpr shared_ptr(nullptr_t) noexcept : shared_ptr() { }
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template<class Y>
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explicit shared_ptr(Y* p);
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template<class Y, class D>
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shared_ptr(Y* p, D d);
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template<class Y, class D, class A>
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shared_ptr(Y* p, D d, A a);
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template<class D>
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shared_ptr(nullptr_t p, D d);
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template<class D, class A>
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shared_ptr(nullptr_t p, D d, A a);
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template<class Y>
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shared_ptr(const shared_ptr<Y>& r, element_type* p) noexcept;
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template<class Y>
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shared_ptr(shared_ptr<Y>&& r, element_type* p) noexcept;
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shared_ptr(const shared_ptr& r) noexcept;
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template<class Y>
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shared_ptr(const shared_ptr<Y>& r) noexcept;
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shared_ptr(shared_ptr&& r) noexcept;
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template<class Y>
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shared_ptr(shared_ptr<Y>&& r) noexcept;
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template<class Y>
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explicit shared_ptr(const weak_ptr<Y>& r);
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template<class Y, class D>
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shared_ptr(unique_ptr<Y, D>&& r);
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// [util.smartptr.shared.dest], destructor
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~shared_ptr();
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// [util.smartptr.shared.assign], assignment
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shared_ptr& operator=(const shared_ptr& r) noexcept;
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template<class Y>
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shared_ptr& operator=(const shared_ptr<Y>& r) noexcept;
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shared_ptr& operator=(shared_ptr&& r) noexcept;
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template<class Y>
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shared_ptr& operator=(shared_ptr<Y>&& r) noexcept;
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template<class Y, class D>
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shared_ptr& operator=(unique_ptr<Y, D>&& r);
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// [util.smartptr.shared.mod], modifiers
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void swap(shared_ptr& r) noexcept;
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void reset() noexcept;
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template<class Y>
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void reset(Y* p);
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template<class Y, class D>
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void reset(Y* p, D d);
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template<class Y, class D, class A>
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void reset(Y* p, D d, A a);
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// [util.smartptr.shared.obs], observers
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element_type* get() const noexcept;
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T& operator*() const noexcept;
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T* operator->() const noexcept;
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element_type& operator[](ptrdiff_t i) const;
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long use_count() const noexcept;
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| 73 |
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explicit operator bool() const noexcept;
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| 74 |
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template<class U>
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bool owner_before(const shared_ptr<U>& b) const noexcept;
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template<class U>
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bool owner_before(const weak_ptr<U>& b) const noexcept;
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};
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template<class T>
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shared_ptr(weak_ptr<T>) -> shared_ptr<T>;
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| 82 |
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template<class T, class D>
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shared_ptr(unique_ptr<T, D>) -> shared_ptr<T>;
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| 84 |
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}
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| 85 |
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```
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| 86 |
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| 87 |
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Specializations of `shared_ptr` shall be *Cpp17CopyConstructible*,
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*Cpp17CopyAssignable*, and *Cpp17LessThanComparable*, allowing their use
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in standard containers. Specializations of `shared_ptr` shall be
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| 90 |
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contextually convertible to `bool`, allowing their use in boolean
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| 91 |
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expressions and declarations in conditions.
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The template parameter `T` of `shared_ptr` may be an incomplete type.
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[*Note 1*: `T` can be a function type. — *end note*]
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[*Example 1*:
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| 98 |
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| 99 |
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``` cpp
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if (shared_ptr<X> px = dynamic_pointer_cast<X>(py)) {
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| 101 |
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// do something with px
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}
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| 103 |
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```
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— *end example*]
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For purposes of determining the presence of a data race, member
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| 108 |
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functions shall access and modify only the `shared_ptr` and `weak_ptr`
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| 109 |
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objects themselves and not objects they refer to. Changes in
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| 110 |
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`use_count()` do not reflect modifications that can introduce data
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| 111 |
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races.
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| 112 |
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| 113 |
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For the purposes of subclause [[smartptr]], a pointer type `Y*` is said
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| 114 |
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to be *compatible with* a pointer type `T*` when either `Y*` is
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| 115 |
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convertible to `T*` or `Y` is `U[N]` and `T` is cv `U[]`.
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