从一个名称空间中调用在多个名称空间中重载的函数 [英] Calling a function overloaded in several namespaces from inside one namespace

问题描述

我有以下代码段:

void foo(double a) {}

namespace bar_space
{
  struct Bar {};

  void foo(Bar a) {}
}

foo(double)是库中的常规函数​​. 我有自己的命名空间bar_space和自己的结构Bar.我想为Bar实现foo()的重载，从而使Bar更类似于内置类型.

foo(double) is a general function from a library. I have my own namespace bar_space with my own struct, Bar. I would like to implement an overloading of foo() for Bar, thus making Bar more similar to the built-in types.

当我尝试从名称空间中调用原始foo(double)时，出现问题:

Trouble appears when I attempt to call the original foo(double) from within the namespace:

namespace bar_space
{
  void baz()
  {
    foo(5.0); // error: conversion from ‘double’ to non-scalar type ‘ssc::bar_space::Bar’ requested
  }
}

在我的Fedora和Mac上的gcc上都无法编译.

This fails to compile on gcc on both my Fedora and Mac.

呼叫

foo(5.0)

从名称空间外部或使用

namespace bar_space
{
  ::foo(5.0)
}

可以正常工作，但这不能使我的新功能达到我的期望(其他开发人员也在bar_space内工作).

works ok, but this doesnt make my new function quite as nice as I had hoped for (other developers are also working inside bar_space).

bar_space是否隐藏了原始功能?有没有一种方法可以使bar()内的foo(5.0)可以在没有显式作用域(::)的情况下被调用?感谢您的帮助.

Is bar_space hiding the original function? Is there a way to make foo(5.0) callable from within bar_space without explicit scoping (::)? Any help is appreciated.

推荐答案

在C ++中，有一个名为

In C++, there is a concept called name hiding. Basically, a function or class name is "hidden" if there is a function/class of the same name in a nested scope. This prevents the compiler from "seeing" the hidden name.

C ++标准的3.3.7节内容为:

Section 3.3.7 of the C++ standard reads:

名称可以由显式隐藏 在一个同名的声明中 嵌套的声明性区域或派生 课(10.2)

A name can be hidden by an explicit declaration of that same name in a nested declarative region or derived class (10.2)

因此，要回答您的问题:在您的示例中，void foo(double a);被void bar_space::foo(Bar a);隐藏了 .因此，您需要使用::作用域确定运算符来调用外部函数.

So, to answer your question: in your example void foo(double a); is hidden by void bar_space::foo(Bar a); So you need to use the :: scoping operator to invoke the outer function.

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