Alias template proxy_view
Class template observer_facade
Header:
proxy.h
Module:proxy
Namespace:pro::inline v4
Since: 3.2.0
template <facade F> struct observer_facade; template <facade F> using proxy_view = proxy<observer_facade<F>>; proxy_view<F> is a non-owning, trivially copyable, trivially relocatable view of an object that models proxiable_target<T, F>. It behaves like a proxy<F> except that it never owns the lifetime of the underlying object.
observer_facade<F> adapts an existing facade F for this non-owning use. The adaptation preserves only those parts of F that remain semantically valid when the storage is reduced to a single pointer and modifies substitution conversions so that view-ness is preserved (substitution that would have produced an owning proxy<G> instead produces a proxy_view<G>).
Member Types of observer_facade
| Name | Description |
|---|---|
convention_types | A tuple-like type transformed from typename F::convention_types. Specifically, for each convention C in typename F::convention_types:- If C::is_direct is false, include C unchanged.- Otherwise, if typename C::dispatch_type is substitution_dispatch, include a transformed convention C' whose* is_direct is true and dispatch_type is still substitution_dispatch.* For every overload O in typename C::overload_types with signature (after cv/ref/noexcept qualifiers) returning a proxy<G>, replace its return type with proxy_view<G> while preserving qualifiers and noexcept.- Otherwise C is discarded. |
reflection_types | A tuple-like type transformed from typename F::reflection_types. Specifically, for each reflection type R in typename F::reflection_types, R is included when R::is_direct is false, or otherwise discarded. |
Member Constants of observer_facade
| Name | Definition |
|---|---|
max_size [static] [constexpr] | sizeof(void*) |
max_align [static] [constexpr] | alignof(void*) |
copyability [static] [constexpr] | constraint_level::trivial |
relocatability [static] [constexpr] | constraint_level::trivial |
destructibility [static] [constexpr] | constraint_level::trivial |
Example
#include <map> #include <proxy/proxy.h> template <class K, class V> struct FMap : pro::facade_builder // ::add_convention<pro::operator_dispatch<"[]">, V&(const K& key)> // ::build {}; int main() { std::map<int, int> v; pro::proxy_view<FMap<int, int>> p = &v; (*p)[1] = 123; printf("%d\n", v.at(1)); // Prints "123" }