proxy

Function template `allocate_proxy_shared`

The definition of allocate_proxy_shared makes use of exposition-only class templates strong-compact-ptr and weak-compact-ptr. Their semantics are similar to std::shared_ptr and std::weak_ptr, but do not provide a polymorphic deleter. Their size and alignment are guaranteed not to be greater than those of a raw pointer type. strong-compact-ptr<T, Alloc> is conditionally convertible to weak-compact-ptr<T, Alloc> only if necessary. Similar to std::optional, strong-compact-ptr<T, Alloc> provides operator* for accessing the managed object of type T with the same qualifiers.

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

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

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

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

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 strong-compact-ptr may vary depending on the definition of F. Specifically, when F does not support weak ownership via basic_facade_builder::support_weak, strong-compact-ptr<T, Alloc> is not convertible to weak-compact-ptr<T, Alloc>, which leaves more room for optimization.

Example

#include <iostream>
#include <memory_resource>

#include "proxy.h"

struct RttiAware : pro::facade_builder
    ::support_copy<pro::constraint_level::nothrow>
    ::support_rtti
    ::build {};

int main() {
  std::pmr::unsynchronized_pool_resource pool;
  std::pmr::polymorphic_allocator<> alloc{&pool};
  pro::proxy<RttiAware> p1 = pro::allocate_proxy_shared<RttiAware>(alloc, 1);
  pro::proxy<RttiAware> p2 = p1;
  proxy_cast<int&>(*p1) += 2;
  std::cout << proxy_cast<int>(*p2) << "\n";  // Prints "3"
}