具有类参数的函数从命名空间泄漏？ [英] Functions with class arguments are leaked from a namespace?

问题描述

我有一小块代码在这里供您考虑，这让我很困惑。奇怪的是，它编译在Sun Studio和GCC上，即使我认为它不应该。

请考虑这：

 命名空间名称
 {
 class C 
 {
 int a; 
}; 
 
 void f（C c）; 
 void g（int a）; 
} 
 
 int main（int argc，char ** argv）
 {
 name :: C c; 
 
 name :: f（c）; 
 f（c）; //< --- this compiles，strangely enough够
 
 name :: g（42）; 
 // g（42）; <--- this does not，as I expected 
} 
  

相同的命名空间导致函数 f 从命名空间中泄漏，并且可以不使用 name :: 访问。 / p>

有没有人有这样的解释？

解决方案

它被称为测量依赖查找（或Koenig查找）。总之，编译器将在命名空间中寻找作为参数类型的命名空间的函数。

I have a small piece of code here for your consideration which puzzles me quite a lot. The strange thing is that it compiles on both Sun Studio and GCC even though I think it should not.

Consider this:

namespace name
{
  class C
    {
      int a;
    };

  void f(C c);
  void g(int a);
}

int main(int argc, char** argv)
{
  name::C c;

  name::f(c); 
  f(c);  // <--- this compiles, strangely enough

  name::g(42);
  // g(42);  <--- this does not, as I expected
}

The class argument from the same namespace causes the function f to 'leak' out of the namespace and be accessible without name::.

Does anybody have an explanation for this? It is certainly me and not the compiler being wrong here.

解决方案

It's called argument-dependent lookup (or Koenig lookup). In short, the compiler will look for the function in namespaces that are the namespaces of argument types.

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