add PtrContainer to manage pointer which is deeply copyable

src/butil/ptr_container.h

+// Copyright (c) 2018 brpc authors.
+// 
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// 
+//     http://www.apache.org/licenses/LICENSE-2.0
+// 
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Author: Ge,Jun (jge666@gmail.com)
+// Date: Fri Sep  7 12:15:23 CST 2018
+
+#ifndef BUTIL_PTR_CONTAINER_H
+#define BUTIL_PTR_CONTAINER_H
+
+namespace butil {
+
+// Manage lifetime of a pointer. The key difference between PtrContainer and
+// unique_ptr is that PtrContainer can be copied and the pointer inside is
+// deeply copied or constructed on-demand.
+template <typename T>
+class PtrContainer {
+public:
+    PtrContainer() : _ptr(NULL) {}
+
+    explicit PtrContainer(T* obj) : _ptr(obj) {}
+
+    ~PtrContainer() {
+        delete _ptr;
+    }
+
+    PtrContainer(const PtrContainer& rhs)
+        : _ptr(rhs._ptr ? new T(*rhs._ptr) : NULL) {}
+    
+    void operator=(const PtrContainer& rhs) {
+        if (rhs._ptr) {
+            if (_ptr) {
+                *_ptr = *rhs._ptr;
+            } else {
+                _ptr = new T(*rhs._ptr);
+            }
+        } else {
+            delete _ptr;
+            _ptr = NULL;
+        }
+    }
+
+    T* get() const { return _ptr; }
+
+    void reset(T* ptr) {
+        delete _ptr;
+        _ptr = ptr;
+    }
+
+    operator void*() const { return _ptr; }
+    
+private:
+    T* _ptr;
+};
+
+}  // namespace butil
+
+#endif  // BUTIL_PTR_CONTAINER_H