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重载一元运算符是否有意义？

[英]Does it ever make sense to overload unary operator &?

原文 2010-10-16 11:16:12 5 6 c++/ operator-overloading

So, C++ allows overloading the unary operator & (address). 因此，C ++允许重载一元运算operator & （地址）。 Are you aware of any real-world example when operator & was rightfully overloaded? 当operator &被正确重载时，您是否了解任何实际示例？ And a second, more specific question, are you aware of any real-world example when operator & was rightfully overloaded while preserving address semantics? 第二个更具体的问题是，在保留地址语义的同时，当operator &被正确重载时，你是否知道任何现实世界的例子？ TIA TIA

6 个解决方案

I've got 207 real-world examples of operator &() : Code search 1 , Code search 2 . 我有207 个 operator &() 真实示例：代码搜索1 ，代码搜索2 。

Including SafeInt<> (to get the underlying naked integer), boost::gil (apparently also to yield the raw data), Mozilla (that say "it is risky to define operator&, but, hey, we know what we're doing."), wxWidgets, Armagetron and lots of more. 包括SafeInt<> （以获取底层裸整数）， boost :: gil （显然也是为了产生原始数据），Mozilla（说“定义运算符有风险，但是，嘿，我们知道我们在做什么。），wxWidgets， Armagetron等等。

It seems some use the iterator idiom &*it to get a raw reference or pointer backwards, and write *&it to get a raw reference and &it to get a raw pointer. 似乎有些人使用迭代器习语&*it来向后获取原始引用或指针，并编写*&it以获取原始引用和&it以获取原始指针。

Notice that once your type overloads operator& and returns something different than the built-in operator, your type is not CopyConstructible anymore (in C++03 - C++0x seems to have lifted it), and so cannot be used as element-type in a Standard container anymore. 请注意，一旦你的类型重载operator&并返回与内置运算符不同的东西，你的类型就不再是CopyConstructible了（在C ++ 03中 - C ++ 0x似乎已经解除了它），因此不能用作元素 -再输入标准容器。

它似乎用于ATL，例如http://msdn.microsoft.com/en-us/library/5s6et3yb.aspx

I don't know of a concrete example off-hand, but I could imagine a container class where you might want to return a smart pointer or an iterator. 我不知道一个具体的例子，但我可以想象一个容器类，你可能想要返回一个智能指针或迭代器。 I'm not saying this necessarily makes sense, though. 不过，我并不是说这必然是有道理的。

One good reason to overload it might be to make it private , to prevent users from using it. 超载它的一个好理由可能是将其设为private ，以防止用户使用它。 I can't this think of any real-world example where you would want to prevent this, but it seems to be the most logical reason to overload it. 我不能想到你想要阻止它的任何现实世界的例子，但它似乎是超载它的最合理的理由。

I did it once when an object had a special-purpose smart pointer. 当一个对象有一个特殊用途的智能指针时，我做了一次。 operator& quietly 'lifted' a stack-allocated object into a heap-based smart pointer version, and this operator behaved differently once the object was inside the pointer. operator&悄悄地将堆栈分配的对象“提升”为基于堆的智能指针版本，并且一旦对象在指针内部，此运算符的行为就会不同。

I don't have the code any more, but there was a reason for it at the time. 我不再有代码，但当时有理由这样做。 It's certainly not a decision to take lightly, this road is lined with corpses. 这显然不是一个轻率的决定，这条道路上布满了尸体。

I overloaded this operator when writing classes for interacting with Direct3D. 在编写用于与Direct3D交互的类时，我重载了此运算符。 It was a smart pointer class that needed to have T** returned from operator& so that it could be used in functions that expect pointer-to-pointer. 这是一个智能指针类，需要从运算符返回T **，以便它可以用于期望指向指针的函数。 T** semantics are rare but you do need them in some situations. T **语义很少见，但在某些情况下确实需要它们。