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Function template allocate_proxy

Header: proxy.h
Module: proxy
Namespace: pro::inline v4

The definition of allocate_proxy makes use of an exposition-only class template allocated-ptr. An object of type allocated-ptr<T, Alloc> allocates the storage for another object of type T with an allocator of type Alloc and manages the lifetime of this contained object. Similar to std::optional, allocated-ptr<T, Alloc> provides operator* for accessing the managed object of type T with the same qualifiers, but does not necessarily support the state where the contained object is absent.

// (1)
template <facade F, class T, class Alloc, class... Args>
proxy<F> allocate_proxy(const Alloc& alloc, Args&&... args);  // freestanding-deleted

// (2)
template <facade F, class T, class Alloc, class U, class... Args>
proxy<F> allocate_proxy(const Alloc& alloc, std::initializer_list<U> il, Args&&... args);  // freestanding-deleted

// (3)
template <facade F, class Alloc, class T>
proxy<F> allocate_proxy(const Alloc& alloc, T&& value);  // freestanding-deleted

(1) Creates a proxy<F> object containing a value p of type allocated-ptr<T, Alloc>, where *p is direct-non-list-initialized with std::forward<Args>(args)....

(2) Creates a proxy<F> object containing a value p of type allocated-ptr<T, Alloc>, where *p is direct-non-list-initialized with il, std::forward<Args>(args)....

(3) Creates a proxy<F> object containing a value p of type allocated-ptr<std::decay_t<T>, Alloc>, where *p is direct-non-list-initialized with std::forward<T>(value).

Since 3.3.0: For (1-3), if proxiable_target<std::decay_t<T>, F> is false, the program is ill-formed and diagnostic messages are generated.

Return Value

The constructed proxy object.

Exceptions

Throws any exception thrown by allocation or the constructor of T.

Notes

The implementation of allocated-ptr may vary depending on the definition of F. Specifically, when F::max_size and F::max_align are not large enough to hold both a pointer to the allocated memory and a copy of the allocator, allocated-ptr shall allocate additional storage for the allocator.

Example

#include <array>

#include <proxy/proxy.h>

// By default, the maximum pointer size defined by pro::facade_builder
// is 2 * sizeof(void*). This value can be overridden by `restrict_layout`.
struct Any : pro::facade_builder::build {};

int main() {
  // sizeof(std::array<int, 100>) is usually greater than 2 * sizeof(void*),
  // calling allocate_proxy has no limitation to the size and alignment of the
  // target
  using Target = std::array<int, 100>;
  pro::proxy<Any> p1 =
      pro::allocate_proxy<Any, Target>(std::allocator<Target>{});
}

See Also