20 General utilities library [utilities]

20.11 Smart pointers [smartptr]

20.11.3 Class template shared_­ptr [util.smartptr.shared]

20.11.3.9 Casts [util.smartptr.shared.cast]

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template<class T, class U> shared_ptr<T> static_pointer_cast(const shared_ptr<U>& r) noexcept; template<class T, class U> shared_ptr<T> static_pointer_cast(shared_ptr<U>&& r) noexcept;
1
#
Mandates: The expression static_­cast<T*>((U*)nullptr) is well-formed.
2
#
Returns: 
shared_ptr<T>(R, static_cast<typename shared_ptr<T>::element_type*>(r.get()))
where R is r for the first overload, and std​::​move(r) for the second.
3
#
[ Note
:
The seemingly equivalent expression shared_­ptr<T>(static_­cast<T*>(r.get())) will eventually result in undefined behavior, attempting to delete the same object twice.
— end note
 ]
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template<class T, class U> shared_ptr<T> dynamic_pointer_cast(const shared_ptr<U>& r) noexcept; template<class T, class U> shared_ptr<T> dynamic_pointer_cast(shared_ptr<U>&& r) noexcept;
4
#
Mandates: The expression dynamic_­cast<T*>((U*)nullptr) is well-formed.
The expression dynamic_­cast<typename shared_­ptr<T>​::​element_­type*>(r.get()) is well formed.
5
#
Preconditions: The expression dynamic_­cast<typename shared_­ptr<T>​::​element_­type*>(r.get()) has well-defined behavior.
6
#
Returns:
  • (6.1)
    When dynamic_­cast<typename shared_­ptr<T>​::​element_­type*>(r.get()) returns a non-null value p, shared_­ptr<T>(R, p), where R is r for the first overload, and std​::​move(r) for the second.
  • (6.2)
    Otherwise, shared_­ptr<T>().
7
#
[ Note
:
The seemingly equivalent expression shared_­ptr<T>(dynamic_­cast<T*>(r.get())) will eventually result in undefined behavior, attempting to delete the same object twice.
— end note
 ]
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template<class T, class U> shared_ptr<T> const_pointer_cast(const shared_ptr<U>& r) noexcept; template<class T, class U> shared_ptr<T> const_pointer_cast(shared_ptr<U>&& r) noexcept;
8
#
Mandates: The expression const_­cast<T*>((U*)nullptr) is well-formed.
9
#
Returns: 
shared_ptr<T>(R, const_cast<typename shared_ptr<T>::element_type*>(r.get()))
where R is r for the first overload, and std​::​move(r) for the second.
10
#
[ Note
:
The seemingly equivalent expression shared_­ptr<T>(const_­cast<T*>(r.get())) will eventually result in undefined behavior, attempting to delete the same object twice.
— end note
 ]
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template<class T, class U> shared_ptr<T> reinterpret_pointer_cast(const shared_ptr<U>& r) noexcept; template<class T, class U> shared_ptr<T> reinterpret_pointer_cast(shared_ptr<U>&& r) noexcept;
11
#
Mandates: The expression reinterpret_­cast<T*>((U*)nullptr) is well-formed.
12
#
Returns: 
shared_ptr<T>(R, reinterpret_cast<typename shared_ptr<T>::element_type*>(r.get()))
where R is r for the first overload, and std​::​move(r) for the second.
13
#
[ Note
:
The seemingly equivalent expression shared_­ptr<T>(reinterpret_­cast<T*>(r.get())) will eventually result in undefined behavior, attempting to delete the same object twice.
— end note
 ]