编译时反射在C ++ 1z？ [英] Compile-time reflection in C++1z?

问题描述

在C ++标准化委员会中有一个研究小组，在C ++ 1z或之后提供编译时反映。

There is a study group in the C++ standardization committee to provide compile-time reflection in C++1z or after. I would like to know what is exactly the purpose and how powerful the expected tools will be?

例如，可以使用这些工具来命名函数或类吗？ / p>

For example will it be possible to name functions or classes using these tools?

struct A {int f() {return 42;}};
struct B {int (std::reflect<A>::member<0>::declname)() {return 43;}};
// equivalent to struct B {int f() {return 43;}};

如果它不像这样强大，典型的用例是什么？

If it would not be as powerful as this, what the typical use cases will be?

推荐答案

反映用例在N3814中概述：

Reflection use cases are outlined in N3814:

http://www.open-std.org/jtc1/sc22/wg21/docs/papers /2013/n3814.html

一般来说，我们将以N3815为例来扩展Type Traits库：

The general view is that we will do it as an extension of the Type Traits library as exemplified by N3815:

http：// www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3815.html

反射有两部分。第一个是内省 。获取一个实体并查询它的常量值。第二个是 reification ，相反，使用值来创建新实体。

There are two parts to reflection. The first is introspection. Taking an entity and querying constant values about it. The second is reification, which is the opposite - using values to create new entities.

对于内省 - 您可以枚举并在编译时获取类成员，基类，枚举器，函数参数等的名称。

For introspection - you can expect additional traits that will allow you to enumerate and get the names of class members, base classes, enumerators, function paramaters and so forth at compile-time. From there you can use them for things like serialization, memberwise operations, static checks and various other things.

此外，我们正在查看reification，这将涉及创建新的实体从具有更多表达力的常量值，你可以用一个模板。所以也许你可以填写一个 std :: class_specifier s 结构，然后调用 make_type_from_spec（s）创建类型。

Additionally later we are looking at reification, which would involve creating new entities from constant values with more expressiveness than you can with a template. So perhaps you might fill out a std::class_specifier s struct and then call make_type_from_spec(s) to create the type.

内省方法目前有更多的共识，资本化程度越来越远。

The introspection approach has more consensus at the moment, the reification side is further off.

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