我可以使用boost :: make_shared与私有构造？ [英] Can I use boost::make_shared with a private constructor?

问题描述

考虑以下几点：

class DirectoryIterator;

namespace detail {
    class FileDataProxy;

    class DirectoryIteratorImpl
    {
        friend class DirectoryIterator;
        friend class FileDataProxy;

        WIN32_FIND_DATAW currentData;
        HANDLE hFind;
        std::wstring root;

        DirectoryIteratorImpl();
        explicit DirectoryIteratorImpl(const std::wstring& pathSpec);
        void increment();
        bool equal(const DirectoryIteratorImpl& other) const;
    public:
        ~DirectoryIteratorImpl() {};
    };

    class FileDataProxy //Serves as a proxy to the WIN32_FIND_DATA struture inside the iterator.
    {
        friend class DirectoryIterator;
        boost::shared_ptr<DirectoryIteratorImpl> iteratorSource;
        FileDataProxy(boost::shared_ptr<DirectoryIteratorImpl> parent) : iteratorSource(parent) {};
    public:
        std::wstring GetFolderPath() const {
            return iteratorSource->root;
        }
    };
}

class DirectoryIterator : public boost::iterator_facade<DirectoryIterator, detail::FileDataProxy, std::input_iterator_tag>
{
    friend class boost::iterator_core_access;
    boost::shared_ptr<detail::DirectoryIteratorImpl> impl;
    void increment() {
        impl->increment();
    };
    bool equal(const DirectoryIterator& other) const {
        return impl->equal(*other.impl);
    };
    detail::FileDataProxy dereference() const {
        return detail::FileDataProxy(impl);
    };
public:
    DirectoryIterator() {
        impl = boost::make_shared<detail::DirectoryIteratorImpl>();
    };
};

好像DirectoryIterator应该能够调用的boost :: make_shared＆LT; D​​irectoryIteratorImpl＆GT; ，因为它是一个朋友 DirectoryIteratorImpl 。然而，这code编译失败，因为DirectoryIteratorImpl的构造函数是私有的。

It seems like DirectoryIterator should be able to call boost::make_shared<DirectoryIteratorImpl>, because it is a friend of DirectoryIteratorImpl. However, this code fails to compile because the constructor for DirectoryIteratorImpl is private.

因为此类是一个内部实现细节的客户 DirectoryIterator 不应该碰，这将是很好，如果我能保持构造私有的。

Since this class is an internal implementation detail that clients of DirectoryIterator should never touch, it would be nice if I could keep the constructor private.

这是我的周围根本误解 make_shared 或做我需要标记某种提振一块为朋友中订购电话编译？

Is this my fundamental misunderstanding around make_shared or do I need to mark some sort of boost piece as friend in order for the call to compile?

推荐答案

您确实需要做一些提升作品的朋友这一点。基本上 make_shared 被调用构造函数，事实上，这是从一个朋友函数内做了编译器没有关系。

You will indeed need to make some boost pieces friend for this. Basically make_shared is calling the constructor and the fact that this is done from within a friend function does not matter for the compiler.

好消息是，虽然 make_shared 被调用构造函数，而不是任何其他棋子。所以只是让 make_shared 的朋友会工作......然而，这意味着任何人都可以再创建一个的shared_ptr＆LT; D​​irectoryIteratorImpl＆GT; 。 ..

The good news though is that make_shared is calling the constructor, not any other piece. So just making make_shared friend would work... However it means that anyone could then create a shared_ptr<DirectoryIteratorImpl>...

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