tmp/tmp0wybuw9r/{from.md → to.md}
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| 1 |
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### Explicit lifetime management <a id="obj.lifetime">[[obj.lifetime]]</a>
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``` cpp
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template<class T>
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T* start_lifetime_as(void* p) noexcept;
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template<class T>
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const T* start_lifetime_as(const void* p) noexcept;
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template<class T>
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volatile T* start_lifetime_as(volatile void* p) noexcept;
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template<class T>
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const volatile T* start_lifetime_as(const volatile void* p) noexcept;
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```
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*Mandates:* `T` is an implicit-lifetime type [[basic.types.general]] and
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not an incomplete type [[term.incomplete.type]].
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*Preconditions:* \[`p`, `(char*)p + sizeof(T)`) denotes a region of
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allocated storage that is a subset of the region of storage reachable
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through [[basic.compound]] `p` and suitably aligned for the type `T`.
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*Effects:* Implicitly creates objects [[intro.object]] within the
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denoted region consisting of an object *a* of type `T` whose address is
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`p`, and objects nested within *a*, as follows: The object
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representation of *a* is the contents of the storage prior to the call
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to `start_lifetime_as`. The value of each created object *o* of
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trivially-copyable type `U` is determined in the same manner as for a
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call to `bit_cast<U>(E)` [[bit.cast]], where `E` is an lvalue of type
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`U` denoting *o*, except that the storage is not accessed. The value of
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any other created object is unspecified.
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[*Note 1*: The unspecified value can be indeterminate. — *end note*]
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*Returns:* A pointer to the *a* defined in the *Effects* paragraph.
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``` cpp
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template<class T>
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T* start_lifetime_as_array(void* p, size_t n) noexcept;
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template<class T>
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const T* start_lifetime_as_array(const void* p, size_t n) noexcept;
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template<class T>
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volatile T* start_lifetime_as_array(volatile void* p, size_t n) noexcept;
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template<class T>
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const volatile T* start_lifetime_as_array(const volatile void* p, size_t n) noexcept;
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```
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*Mandates:* `T` is a complete type.
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*Preconditions:* `p` is suitably aligned for an array of `T` or is null.
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`n <= size_t(-1) / sizeof(T)` is `true`. If `n > 0` is `true`,
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\[`(char*)p`, `(char*)p + (n * sizeof(T))`) denotes a region of
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allocated storage that is a subset of the region of storage reachable
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through [[basic.compound]] `p`.
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*Effects:* If `n > 0` is `true`, equivalent to `start_lifetime_as<U>(p)`
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where `U` is the type “array of `n` `T`”. Otherwise, there are no
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effects.
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*Returns:* A pointer to the first element of the created array, if any;
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otherwise, a pointer that compares equal to `p` [[expr.eq]].
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