使用即将推出的 C++ 反射工具打印类型的全名 [英] Using the upcoming C++ reflection facilities to print the full name of a type

问题描述

目前可以使用__PRETTY_FUNCTION__在gcc和clang下显示模板类型:

Currently, one can use __PRETTY_FUNCTION__ to display a template type under gcc, and clang:

#include <iostream>

template <class T>
void print_type() {
  std::cout << __PRETTY_FUNCTION__ << std::endl;
}

int main(int argc, char* argv[]) {
  print_type<const volatile int&>();
  return 0;
}

将输出:

void print_type() [with T = const volatile int&]

随着 reflection TS 的到来和 C++ 中的反射设施，我被想知道能够执行类似操作的语法是什么样的.

With the reflection TS coming and reflection facilities in C++, I was wondering what the syntax would look like to be able to do something similar.

注意:由于反射 TS 还没有被投票，我只是在寻找一个可能的"语法.

Note: as the reflection TS has not been voted in yet, I am only looking for a "probable" syntax.

推荐答案

猜测是这样的:

template <class T>
void print_type() {
    using F = reflexpr(print_type<T>);
    std::cout << get_display_name_v<F> << std::endl;
}

你必须reflexpr一个特定的东西，没有办法得到我发现自己处于这个功能" - 所以那就是print_type.然后文档只是说这是实现定义的.

You have to reflexpr a specific thing, there's no way to get "this function I find myself in" - so that's print_type<T>. And then the documentation just says that this is implementation defined.

如果你想把它全部写出来，你可以这样做:

If you want to write it all out, you can do:

template <class T>
void print_type() {
    std::cout << "void "
              << get_name_v<reflexpr(print_type<T>)> // guaranteed "print_type"
              << "() [with T = "
              << get_display_name_v<reflexpr(T)> 
              << "]" << std::endl;
}

我不清楚 get_name_v 实际上是什么.似乎它可能是空的 - T 在这种情况下不是 simple-type-specifier)并且没有提到 cv- 或 ref-限定符，这就是为什么我使用了 get_display_name_v.

It's unclear to me what get_name_v<reflexpr(const volatile int&)> actually is. It seems like it's probably empty - T is not a simple-type-specifier in this case) and there is no mention of cv- or ref-qualifiers, which is why I used get_display_name_v.

请注意，反射 TS 是基于类型的 - 每个 reflexpr 都为您提供一个类型，您必须在其中进行基于类型的元编程.语言本身最终可能采用的方法是 value-based 反射 - 即 reflexpr 产生一小组预定义反射对象类型的值.这将使实际编码更容易，这就是为什么我们在工作中喜欢 constexpr! 和支持 constexpr 分配的原因.

Note that the Reflection TS is type-based - each reflexpr gives you a type that you have to do type-based metaprogramming in. The approach the language itself will likely end up with is value-based reflection - that is reflexpr yields a value of a small set of predefined reflection object types. This will make it easier to actually code, and is why we papers like constexpr! and support for constexpr allocation in the works.

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