C++核心准则C.81:如果不需要默认（同时不需要其他选项）行为，使用=delete禁止它们

C.81: Use =delete when you want to disable default behavior (without wanting an alternative)

C.81:如果不需要默认（同时不需要其他选项）行为，使用=delete禁止它们

Reason（原因）

In a few cases, a default operation is not desirable.

某些情况下·，也有可能·不希望存在默认行为。

Example（示例）

class Immortal {
public:
    ~Immortal() = delete;   // do not allow destruction
    // ...
};

void use()
{
    Immortal ugh;   // error: ugh cannot be destroyed
    Immortal* p = new Immortal{};
    delete p;       // error: cannot destroy *p
}

Example（示例）

A unique_ptr can be moved, but not copied. To achieve that its copy operations are deleted. To avoid copying it is necessary to =delete its copy operations from lvalues:

独占指针可以被移动，但是不能被拷贝。为了实现这一点，代码禁止了拷贝操作。禁止拷贝的方法是将源自左值的拷贝操作声明为=delete。

template <class T, class D = default_delete<T>> class unique_ptr {
public:
    // ...
    constexpr unique_ptr() noexcept;
    explicit unique_ptr(pointer p) noexcept;
    // ...
    unique_ptr(unique_ptr&& u) noexcept;   // move constructor
    // ...
    unique_ptr(const unique_ptr&) = delete; // disable copy from lvalue
    // ...
};

unique_ptr<int> make();   // make "something" and return it by moving

void f()
{
    unique_ptr<int> pi {};
    auto pi2 {pi};      // error: no move constructor from lvalue
    auto pi3 {make()};  // OK, move: the result of make() is an rvalue
}

Note that deleted functions should be public.

注意：禁止的函数应该是公有的。

按照惯例，被删除函数（deleted functions）声明为public，而不是private。当用户代码尝试调用一个成员函数时，C++会在检查它的删除状态位之前检查它的可获取性(accessibility，即是否为public？)。当用户尝试调用一个声明为private的删除函数时，一些编译器会抱怨这些删除的函数被声明为private

----Effective Modern C++

Enforcement（实施建议）

The elimination of a default operation is (should be) based on the desired semantics of the class. Consider such classes suspect, but maintain a "positive list" of classes where a human has asserted that the semantics is correct.

消除默认操作（应该）应该基于类的期待语义。怀疑这些类，但同时维护类的“正面清单”，其内容是由人断定是正确的东西。

原文链接

https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c81-use-delete-when-you-want-to-disable-default-behavior-without-wanting-an-alternative

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