c++ - 在编写 C++ 成员定义时，是否有任何理由更喜欢将它们放在命名空间块中而不是完全限定它们，反之亦然？

Question

在 C++ 类中，我们可以用两种风格中的任何一种来编写我们的成员。我们可以将它们放在命名空间块内，或者我们可以完全限定每个。

有什么理由更喜欢一种风格而不是另一种风格？

头文件如下所示（bar.h）：

namespace foo
{
    class Bar
    {
    public:
        Bar();
        int Beans();
    };
}

样式 1 (bar.cpp) -命名空间块内的声明：

#include "bar.h"
namespace foo
{
    Bar::Bar()
    {
    }

    int Bar::Beans()
    {
    }
}

样式 2 (bar.cpp) -完全限定声明：

#include "bar.h"

foo::Bar::Bar()
{
}

int foo::Bar::Beans()
{
}

所以我的问题，再次，是：有什么理由更喜欢一种风格而不是另一种风格？

Answer 1

Here's a possible answer that was posted by James Kanze in answer to another similar question. (edit: note from the comment thread, this only applies to non-member functions).

Prefer the fully qualified form (style 2).

Functions written in this style are explicitly a definition, not a declaration.

That is to say, using Style 2, if you accidentally define a function with incorrect arguments, you'll get a compiler error alerting you to that fact.

Using Style 1, if you define a function with incorrect arguments it will define a different function. It will compile fine, but you'll get a linker error explaining that the method is not defined. This will probably be harder to diagnose than the compiler error resulting from Style 2.