20 Memory management library [mem]

20.3 Smart pointers [smartptr]

20.3.1 Unique-ownership pointers [unique.ptr]

20.3.1.3 unique_ptr for single objects [unique.ptr.single]

20.3.1.3.2 Constructors [unique.ptr.single.ctor]

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constexpr unique_ptr() noexcept; constexpr unique_ptr(nullptr_t) noexcept;
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Constraints: is_pointer_v<deleter_type> is false and is_default_constructible_v<deleter_type> is true.
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Preconditions: D meets the Cpp17DefaultConstructible requirements (Table 30), and that construction does not throw an exception.
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Effects: Constructs a unique_ptr object that owns nothing, value-initializing the stored pointer and the stored deleter.
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Postconditions: get() == nullptr.
get_deleter() returns a reference to the stored deleter.
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constexpr explicit unique_ptr(type_identity_t<pointer> p) noexcept;
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Constraints: is_pointer_v<deleter_type> is false and is_default_constructible_v<deleter_type> is true.
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Preconditions: D meets the Cpp17DefaultConstructible requirements (Table 30), and that construction does not throw an exception.
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Effects: Constructs a unique_ptr which owns p, initializing the stored pointer with p and value-initializing the stored deleter.
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Postconditions: get() == p.
get_deleter() returns a reference to the stored deleter.
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constexpr unique_ptr(type_identity_t<pointer> p, const D& d) noexcept; constexpr unique_ptr(type_identity_t<pointer> p, remove_reference_t<D>&& d) noexcept;
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Constraints: is_constructible_v<D, decltype(d)> is true.
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Preconditions: For the first constructor, if D is not a reference type, D meets the Cpp17CopyConstructible requirements and such construction does not exit via an exception.
For the second constructor, if D is not a reference type, D meets the Cpp17MoveConstructible requirements and such construction does not exit via an exception.
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Effects: Constructs a unique_ptr object which owns p, initializing the stored pointer with p and initializing the deleter from std​::​forward<decltype(d)>(d).
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Postconditions: get() == p.
get_deleter() returns a reference to the stored deleter.
If D is a reference type then get_deleter() returns a reference to the lvalue d.
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Remarks: If D is a reference type, the second constructor is defined as deleted.
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[Example 1: D d; unique_ptr<int, D> p1(new int, D()); // D must be Cpp17MoveConstructible unique_ptr<int, D> p2(new int, d); // D must be Cpp17CopyConstructible unique_ptr<int, D&> p3(new int, d); // p3 holds a reference to d unique_ptr<int, const D&> p4(new int, D()); // error: rvalue deleter object combined // with reference deleter type — end example]
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constexpr unique_ptr(unique_ptr&& u) noexcept;
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Constraints: is_move_constructible_v<D> is true.
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Preconditions: If D is not a reference type, D meets the Cpp17MoveConstructible requirements (Table 31).
Construction of the deleter from an rvalue of type D does not throw an exception.
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Effects: Constructs a unique_ptr from u.
If D is a reference type, this deleter is copy constructed from u's deleter; otherwise, this deleter is move constructed from u's deleter.
[Note 1: 
The construction of the deleter can be implemented with std​::​forward<D>.
— end note]
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Postconditions: get() yields the value u.get() yielded before the construction.
u.get() == nullptr.
get_deleter() returns a reference to the stored deleter that was constructed from u.get_deleter().
If D is a reference type then get_deleter() and u.get_deleter() both reference the same lvalue deleter.
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template<class U, class E> constexpr unique_ptr(unique_ptr<U, E>&& u) noexcept;
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Constraints:
  • (19.1)
    unique_ptr<U, E>​::​pointer is implicitly convertible to pointer,
  • (19.2)
    U is not an array type, and
  • (19.3)
    either D is a reference type and E is the same type as D, or D is not a reference type and E is implicitly convertible to D.
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Preconditions: If E is not a reference type, construction of the deleter from an rvalue of type E is well-formed and does not throw an exception.
Otherwise, E is a reference type and construction of the deleter from an lvalue of type E is well-formed and does not throw an exception.
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Effects: Constructs a unique_ptr from u.
If E is a reference type, this deleter is copy constructed from u's deleter; otherwise, this deleter is move constructed from u's deleter.
[Note 2: 
The deleter constructor can be implemented with std​::​forward<E>.
— end note]
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Postconditions: get() yields the value u.get() yielded before the construction.
u.get() == nullptr.
get_deleter() returns a reference to the stored deleter that was constructed from u.get_deleter().