From 74bb9cd27242b9320f99ff4d2b50c3051576cc14 Mon Sep 17 00:00:00 2001
From: crupest <crupest@outlook.com>
Date: Tue, 8 Feb 2022 16:53:51 +0800
Subject: ...

---
 include/cru/common/SelfResolvable.h | 69 +++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 include/cru/common/SelfResolvable.h

(limited to 'include/cru/common/SelfResolvable.h')

diff --git a/include/cru/common/SelfResolvable.h b/include/cru/common/SelfResolvable.h
new file mode 100644
index 00000000..c8acd4b9
--- /dev/null
+++ b/include/cru/common/SelfResolvable.h
@@ -0,0 +1,69 @@
+#pragma once
+#include "PreConfig.h"
+
+#include <memory>
+#include <type_traits>
+
+namespace cru {
+template <typename T>
+class SelfResolvable;
+
+template <typename T>
+class ObjectResolver {
+  friend SelfResolvable<T>;
+
+ private:
+  ObjectResolver(const std::shared_ptr<T*>& resolver) : resolver_(resolver) {}
+
+ public:
+  ObjectResolver(const ObjectResolver&) = default;
+  ObjectResolver& operator=(const ObjectResolver&) = default;
+  ObjectResolver(ObjectResolver&&) = default;
+  ObjectResolver& operator=(ObjectResolver&&) = default;
+  ~ObjectResolver() = default;
+
+  T* Resolve() const {
+    // resolver_ is null only when this has been moved.
+    // You shouldn't resolve a moved resolver. So assert it.
+    Expects(resolver_);
+    return *resolver_;
+  }
+
+ private:
+  std::shared_ptr<T*> resolver_;
+};
+
+template <typename T>
+class SelfResolvable {
+ public:
+  SelfResolvable() : resolver_(new T*(static_cast<T*>(this))) {}
+  SelfResolvable(const SelfResolvable&) = delete;
+  SelfResolvable& operator=(const SelfResolvable&) = delete;
+
+  // Resolvers to old object will resolve to new object.
+  SelfResolvable(SelfResolvable&& other)
+      : resolver_(std::move(other.resolver_)) {
+    (*resolver_) = static_cast<T*>(this);
+  }
+
+  // Old resolvers for this object will resolve to nullptr.
+  // Other's resolvers will now resolve to this.
+  SelfResolvable& operator=(SelfResolvable&& other) {
+    if (this != &other) {
+      (*resolver_) = nullptr;
+      resolver_ = std::move(other.resolver_);
+      (*resolver_) = static_cast<T*>(this);
+    }
+    return *this;
+  }
+
+  virtual ~SelfResolvable() {
+    if (resolver_ != nullptr) (*resolver_) = nullptr;
+  }
+
+  ObjectResolver<T> CreateResolver() { return ObjectResolver<T>(resolver_); }
+
+ private:
+  std::shared_ptr<T*> resolver_;
+};
+}  // namespace cru
-- 
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