使用std :: unique的静态函数deleter时出错

我有下面的代码片段，无法编译......看起来应该是这样，但它现在回避我。 非常感谢任何帮助/建议！

#include <atomic>
#include <memory>

struct MyClass {

static void free_lock(std::atomic<int>** lck) { (*lck)->store(0); }

typedef std::unique_ptr<std::atomic<int>*, decltype(&MyClass::free_lock)> lock_scope;

static lock_scope get_lock() {
    static std::atomic<int> lck(0);
    int ref = 0;
    return lock_scope(&lck, &MyClass::free_lock);
}

};

Clang 3.2报告了以下错误消息

Compilation finished with errors:
source.cpp:13:23: error: no matching constructor for initialization of 'lock_scope' (aka 'unique_ptr *, decltype(&MyClass::free_lock)>')
        return lock_scope(&lck, &MyClass::free_lock);
                         ^          ~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:130:7: note: candidate constructor not viable: no known conversion from 'std::atomic *' to 'pointer' (aka 'std::atomic **') for 1st argument
      unique_ptr(pointer __p,
      ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:125:7: note: candidate constructor not viable: no known conversion from 'std::atomic *' to 'pointer' (aka 'std::atomic **') for 1st argument
      unique_ptr(pointer __p,
      ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:155:2: note: candidate constructor template not viable: requires single argument '__u', but 2 arguments were provided
        unique_ptr(unique_ptr&& __u) noexcept
        ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:164:2: note: candidate constructor template not viable: requires single argument '__u', but 2 arguments were provided
        unique_ptr(auto_ptr&& __u) noexcept
        ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:114:17: note: candidate constructor not viable: requires 0 arguments, but 2 were provided
      constexpr unique_ptr() noexcept
                ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:120:7: note: candidate constructor not viable: requires single argument '__p', but 2 arguments were provided
      unique_ptr(pointer __p) noexcept
      ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:136:17: note: candidate constructor not viable: requires 1 argument, but 2 were provided
      constexpr unique_ptr(nullptr_t) noexcept
                ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:142:7: note: candidate constructor not viable: requires single argument '__u', but 2 arguments were provided
      unique_ptr(unique_ptr&& __u) noexcept
      ^
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../../include/c++/4.7/bits/unique_ptr.h:262:7: note: candidate constructor not viable: requires 1 argument, but 2 were provided
      unique_ptr(const unique_ptr&) = delete;
      ^
1 error generated.

---

你的lock_scope类型被声明为包装指向std::atomic<int>*的指针，即std::atomic<int>** 。 free_lock声明和定义正确地反映了这一点。

但是，然后你尝试用指向std::atomic<int>的指针初始化lock_scope （少一个间接lock_scope ）。

编译器消息很清楚地表明：

[...] candidate constructor not viable: 
no known conversion from 'std::atomic *' to 'pointer' (aka 'std::atomic **') [...]

您要么为包装的lck需要额外的间接lock_scope ， free_lock将lock_scope和free_lock更改为少用一个间接free_lock 。

---

你可以转换返回lock_scope（..）; 返回std :: move（lock_scope（...））;

因为std :: unique_ptr :: operator =（const std :: unique_ptr＆）是私有的;

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