rocksdb/thrift/lib/cpp/util/shared_ptr_util.h

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/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.
*/
#ifndef THRIFT_UTIL_SHARED_PTR_UTIL_H_
#define THRIFT_UTIL_SHARED_PTR_UTIL_H_ 1
#include <boost/shared_ptr.hpp>
#include <boost/type_traits/is_convertible.hpp>
#include <boost/utility/enable_if.hpp>
/**
* Helper macros to allow function overloading even when using
* boost::shared_ptr.
*
* shared_ptr makes overloading really annoying, since shared_ptr defines
* constructor methods to allow one shared_ptr type to be constructed from any
* other shared_ptr type. (Even if it would be a compile error to actually try
* to instantiate the constructor.) These macros add an extra argument to the
* function to cause it to only be instantiated if a pointer of type T is
* convertible to a pointer of type U.
*
* THRIFT_OVERLOAD_IF should be used in function declarations.
* THRIFT_OVERLOAD_IF_DEFN should be used in the function definition, if it is
* defined separately from where it is declared.
*/
#define THRIFT_OVERLOAD_IF_DEFN(T, Y) \
typename ::boost::enable_if<typename ::boost::is_convertible<T*, Y*>::type, \
void*>::type
#define THRIFT_OVERLOAD_IF(T, Y) \
THRIFT_OVERLOAD_IF_DEFN(T, Y) = NULL
namespace apache { namespace thrift {
/**
* A helper functor that can be used as a shared_ptr destructor, but that does
* nothing at all.
*
* This can be used to create a shared_ptr to an object that shouldn't really
* be destroyed when the last shared_ptr to it goes away. This is useful in
* some situations to call thrift APIs that require a shared_ptr argument when
* you have an object on the stack or otherwise owned by some other part of the
* code.
*
* WARNING: If at all possible, please avoid using this class to create
* shared_ptr. Attempting to use shared_ptrs with manually managed objects is
* generally a bad idea. This class should only be used in a few rare cases
* where a temporary shared_ptr is needed, and you can guarantee that all
* shared_ptrs to the object will be destroyed before the object itself is
* destroyed.
*/
template<class T>
class NoopPtrDestructor {
public:
void operator()(T* obj) {};
};
}} // apache::thrift
#endif // THRIFT_UTIL_SHARED_PTR_UTIL_H_