编辑:更新的坏链接截至2017年2月7日。

我想没有人提到这一点:

在CERN，他们使用c++的全反射系统:

欧洲核子研究中心的反射。看起来效果很好。

I did something like what you're after once, and while it's possible to get some level of reflection and access to higher-level features, the maintenance headache might not be worth it. My system was used to keep the UI classes completely separated from the business logic through delegation akin to Objective-C's concept of message passing and forwarding. The way to do it is to create some base class that is capable of mapping symbols (I used a string pool but you could do it with enums if you prefer speed and compile-time error handling over total flexibility) to function pointers (actually not pure function pointers, but something similar to what Boost has with Boost.Function--which I didn't have access to at the time). You can do the same thing for your member variables as long as you have some common base class capable of representing any value. The entire system was an unabashed ripoff of Key-Value Coding and Delegation, with a few side effects that were perhaps worth the sheer amount of time necessary to get every class that used the system to match all of its methods and members up with legal calls: 1) Any class could call any method on any other class without having to include headers or write fake base classes so the interface could be predefined for the compiler; and 2) The getters and setters of the member variables were easy to make thread-safe because changing or accessing their values was always done through 2 methods in the base class of all objects.

It also led to the possibility of doing some really weird things that otherwise aren't easy in C++. For example I could create an Array object that contained arbitrary items of any type, including itself, and create new arrays dynamically by passing a message to all array items and collecting the return values (similar to map in Lisp). Another was the implementation of key-value observing, whereby I was able to set up the UI to respond immediately to changes in the members of backend classes instead of constantly polling the data or unnecessarily redrawing the display.

也许您更感兴趣的是，您还可以转储为类定义的所有方法和成员，而且是字符串形式。

该系统的缺点可能会让您望而却步:添加所有消息和键值非常繁琐;它比没有反射要慢;你会讨厌看到boost::static_pointer_cast和boost::dynamic_pointer_cast遍布你的代码库;强类型系统的局限性仍然存在，您实际上只是将它们隐藏了一些，所以它不那么明显。字符串中的错别字也不是一个有趣或容易发现的惊喜。

As to how to implement something like this: just use shared and weak pointers to some common base (mine was very imaginatively called "Object") and derive for all the types you want to use. I'd recommend installing Boost.Function instead of doing it the way I did, which was with some custom crap and a ton of ugly macros to wrap the function pointer calls. Since everything is mapped, inspecting objects is just a matter of iterating through all of the keys. Since my classes were essentially as close to a direct ripoff of Cocoa as possible using only C++, if you want something like that then I'd suggest using the Cocoa documentation as a blueprint.

在我的c++生涯中，我知道的两个类似反射的解决方案是:

1)使用RTTI，如果你能够从一个“对象”基类派生所有的类，它将为你提供一个引导来构建类似反射的行为。该类可以提供一些方法，如GetMethod, GetBaseClass等。至于这些方法是如何工作的，你需要手动添加一些宏来装饰你的类型，这些宏在幕后创建类型的元数据，为GetMethods等提供答案。

2)如果你可以访问编译器对象，另一个选择是使用DIA SDK。如果我没记错的话，这允许您打开pdbs，其中应该包含c++类型的元数据。也许足够做你想做的事了。例如，本页展示了如何获取类的所有基类型。

这两种解决方案都有点难看!没有什么比c++更能让你欣赏c#的奢华了。

祝你好运。

在c++中反射是非常有用的，如果你需要为每个成员运行一些方法(例如:序列化，哈希，比较)。我给出了通用的解决方案，语法非常简单:

struct S1
{
    ENUMERATE_MEMBERS(str,i);
    std::string str;
    int i;
};
struct S2
{
    ENUMERATE_MEMBERS(s1,i2);
    S1 s1;
    int i2;
};

其中ENUMERATE_MEMBERS是一个宏，稍后将描述(UPDATE):

假设我们已经为int和std::string定义了序列化函数，如下所示:

void EnumerateWith(BinaryWriter & writer, int val)
{
    //store integer
    writer.WriteBuffer(&val, sizeof(int));
}
void EnumerateWith(BinaryWriter & writer, std::string val)
{
    //store string
    writer.WriteBuffer(val.c_str(), val.size());
}

我们在“secret宏”附近有一个泛型函数;)

template<typename TWriter, typename T>
auto EnumerateWith(TWriter && writer, T && val) -> is_enumerable_t<T>
{
    val.EnumerateWith(write); //method generated by ENUMERATE_MEMBERS macro
}

现在你可以写

S1 s1;
S2 s2;
//....
BinaryWriter writer("serialized.bin");

EnumerateWith(writer, s1); //this will call EnumerateWith for all members of S1
EnumerateWith(writer, s2); //this will call EnumerateWith for all members of S2 and S2::s1 (recursively)

因此在结构定义中有ENUMERATE_MEMBERS宏，你可以构建序列化、比较、散列和其他东西，而不需要触及原始类型，唯一的要求是为每个枚举器(如BinaryWriter)实现每个类型的“EnumerateWith”方法，这是不可枚举的。通常你必须实现10-20个“简单”类型来支持项目中的任何类型。

这个宏在运行时创建/销毁结构的开销应该为零，并且T.EnumerateWith()的代码应该按需生成，这可以通过使其成为模板内联函数来实现，因此所有故事中唯一的开销是向每个结构添加ENUMERATE_MEMBERS(m1,m2,m3…)，而在任何解决方案中，每个成员类型实现特定的方法都是必须的，因此我不认为这是开销。

更新: ENUMERATE_MEMBERS宏有一个非常简单的实现(但是可以稍微扩展以支持从可枚举结构继承)

#define ENUMERATE_MEMBERS(...) \
template<typename TEnumerator> inline void EnumerateWith(TEnumerator & enumerator) const { EnumerateWithHelper(enumerator, __VA_ARGS__ ); }\
template<typename TEnumerator> inline void EnumerateWith(TEnumerator & enumerator) { EnumerateWithHelper(enumerator, __VA_ARGS__); }

// EnumerateWithHelper
template<typename TEnumerator, typename ...T> inline void EnumerateWithHelper(TEnumerator & enumerator, T &...v) 
{ 
    int x[] = { (EnumerateWith(enumerator, v), 1)... }; 
}

// Generic EnumerateWith
template<typename TEnumerator, typename T>
auto EnumerateWith(TEnumerator & enumerator, T & val) -> std::void_t<decltype(val.EnumerateWith(enumerator))>
{
    val.EnumerateWith(enumerator);
}

这15行代码不需要任何第三方库;)

编辑:更新的坏链接截至2017年2月7日。

我想没有人提到这一点:

在CERN，他们使用c++的全反射系统:

欧洲核子研究中心的反射。看起来效果很好。

如果你像这样声明一个指向函数的指针:

int (*func)(int a, int b);

您可以像这样在内存中为该函数分配一个位置(需要libdl和dlopen)

#include <dlfcn.h>

int main(void)
{
    void *handle;
    char *func_name = "bla_bla_bla";
    handle = dlopen("foo.so", RTLD_LAZY);
    *(void **)(&func) = dlsym(handle, func_name);
    return func(1,2);
}

要使用间接方式加载局部符号，可以对调用二进制文件(argv[0])使用dlopen。

这样做的唯一要求(除了dlopen()、libdl和dlfcn.h)是知道函数的参数和类型。