为什么类成员函数影子使用相同名称的自由函数？ [英] Why class member functions shadow free functions with same name?

问题描述

我最近来到我的注意，成员函数完全 在类中有相同名称的自由函数。而完全地，我的意思是每个自由功能具有相同的名称不考虑重载分辨率。我可以理解为什么它做这样的事情：

It recently came to my attention that member functions completely shadow free functions with the same name when inside the class. And by completely i mean that every free function with the same name is not considered for overload resolution at all. I can understand why it's done with somwthing like this:

void f();

struct S
{
    void f();

    void g()
    {
        f(); // calls S::f instead of ::f
    }
};

其中函数具有相同的签名，其唯一自然的变量范围工作方式相同。但为什么禁止unbigious调用，其中自由函数有不同的签名，如下：

where the functions have identical signatures, its only natural as variable scoping works the same way. But why prohibit unambigious calls where free function has different signature like this:

void f();

struct S
{
    void f(int x);

    void g()
    {
        f(); // fails to compile attempting to call S::f, which has wrong signature
    }
};

我不是在询问如何调用类。我想知道的是这个设计背后的理由。

I am not asking how to call a shadowed free function from inside the class. What i want to know is the rationale behind this design.

推荐答案

对于非限定名称查找，一次只能考虑一个范围，如果该范围内的搜索不产生任何结果，下一个较高的范围被搜索。在你的情况下，只搜索 S 的范围。

For unqualified name lookup, only one scope at a time is considered, and if the search in that scope doesn't yield any results, the next higher scope is searched. In your case, only S's scope is searched.

unbigious调用，其中自由函数具有不同的签名，如下：

But why prohibit unambigious calls where free function has different signature like this:

问题是名称查找只关心名称​​标识符。这是完全不知道的事实，你想调用一个函数，它只是看到一个标识符。如果你只是使用 auto x = f; ，如果你这样想，同样的名称查找发生，有很好的理由你只想要一个非常有限的范围搜索。其他任何事情只会让用户惊喜。

The problem is that name lookup doesn't concern itself with anything but the name, the identifier. It is completely oblivious to the fact that you want to call a function, it just sees an identifier. The same name lookup happens if you just use auto x = f;, and if you think of it that way, there are very good reasons you only want a very limited scope to search. Anything else would just surprise the user.

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