Find alternatives to the current C++ smart pointers implementation based on loki

[javarias]

The current C++ smart pointer is based on loki libraries, see .
In modern C++ standards (C++11 and C++17 ) a new set of standard smart pointers have been accepted and introduced as part of the C++ standard libraries, which are listed . The modern C++ standards are support in newer versions of GCC than the one include in CentOS 6, for this reason we should look for an alternative until CentOS and/or RHEL supports the newer compilers.

The C++ smart pointers are mostly based on versions of smart pointers developed by , which should be compatible with the newest C++ standards, providing a simple upgrade path to C++ smart pointers when time comes.

[patbrandt]

In Boost 1.41, there is an implementation of unique_ptr hiding in boost/interprocess/smart_ptr/unique_ptr.hpp. It does not have move semantics, and in fact it seems to support the same copy semantics that auto_ptr does (transferred ownership). But on the plus side it does support custom deleters (which are very useful), and it has the same interface as the C++11 STL version. In later versions of boost it is in movelib (boost/move/unique_ptr.hpp).

There is also an implementation of shared_ptr in the same place, though you can also get that from TR1 in STL (<tr1/shared_ptr>, std::tr1::shared_ptr).

[patbrandt]

The header below attempts to alias a version of unique_ptr, shared_ptr, and weak_ptr under a namespace (acs) to prevent global pollution. I've tested it successfully on RHEL6.7 with:

• gcc4.4.7 with Boost 1.41
• gcc4.4.7 with -std=c++0x
• gcc5.2 with Boost 1.59
• gcc5.2 with -std=c++11

And it (correctly) fails to provide unique_ptr while still supporting the other two on RHEL5.3 with gcc4.1.2 and Boost 1.33. One caveat: unfortunately the boost::interprocess::unique_ptr (Boost 1.35 through 1.56) requires a deleter to specified; there is no default. It's easy enough to define one though:

template <typename T>
void deleter(T *t) {
    delete t;
}

And then all the uses would look like:

acs::unique_ptr<TYPE, void(*)(TYPE*)> up(new TYPE, deleter<TYPE>);

A little unwieldy but this is all-around hacky anyways.

#ifndef modernSmartPtrs_H
#define modernSmartPtrs_H

#include <boost/version.hpp>
#define GCC_VERSION (__GNUC__ * 10000       \
                     + __GNUC_MINOR__ * 100 \
                     + __GNUC_PATCHLEVEL__)

// If C++11 is available, use the STL implementation
#if __cplusplus >= 201103L || \
    (__GNUC__ >= 4 && __GNUC_MINOR__ >= 4 && defined(__GXX_EXPERIMENTAL_CXX0X__)) || \
    defined(__clang__)
#include <memory>
// Pack these into a namespace so they are not polluting globally
// when this header is included.
namespace acs {
using std::unique_ptr;
using std::shared_ptr;
using std::weak_ptr;
}// namespace acs

// Otherwise, fall back on the newest version of boost's
// implementation available
#elif defined(BOOST_VERSION)
// unique_ptr changed places in Boost 1.57, so determine
// where we should look for it
#if BOOST_VERSION >= 105700
#include <boost/move/unique_ptr.hpp>
namespace acs {
using boost::movelib::unique_ptr;
}// namespace acs
#elif BOOST_VERSION >= 103500
#include <boost/interprocess/smart_ptr/unique_ptr.hpp>
namespace acs {
using boost::interprocess::unique_ptr;
}// namespace acs
// If an older version of boost is found, simply omit unique_ptr support
#else
#warning "Using Boost older than 1.35; unique_ptr will not be available!"
#endif//BOOST_VERSION comparison

// Alias shared_ptr and weak_ptr as well
#include <boost/shared_ptr.hpp>
#include <boost/weak_ptr.hpp>
namespace acs {
using boost::shared_ptr;
using boost::weak_ptr;
}// namespace acs

// If we don't have C++11 or Boost, call it an error
// (It might be possible to fall back on TR1, but honestly
// trying to support all that logic for all the GCC versions
// is too much work. Setting the min version of GCC at 4.4 and/or
// Boost at 1.35 is more than reasonable.)
#else
#error "Upgrade your GCC version or install Boost to use this header!"
#endif//__cplusplus[...]

#undef GCC_VERSION

#endif//modernSmartPtrs_H