在编译时的C ++类型注册技巧 [英] C++ type registration at compile time trick
问题描述
我有以下情况:假设我有一堆类型(functors),我想在编译期间注册/编译,最好是类似boost :: mpl :: vector。
你知道有什么好办法吗?
I have the following situation: suppose I have a bunch of types (functors) which I want to register/compile in during compilation, preferably into something like boost::mpl::vector. Do you know any trick to do so nicely?
我的愿望是有一个hpp文件实现functor类型和注册文件,其中一个宏带来类型
My desire is to have hpp file which implements functor type and registration file, where a macro brings in type into compilation.
例如
// registered.hpp
REGISTER("functor1.hpp") // implementation
REGISTER("functor2.hpp")
...
boost::mpl::vector<...> types; // full registration vector
希望它有意义。
谢谢
Hopefully it makes sense. Thank you
推荐答案
有一种方法可以一个一个地注册类型,然后检索所有的形式的mpl :: vector或类似的。我已经学会了这个技巧在助推邮件列表(也许从Dave亚伯拉罕,虽然我不记得肯定)。
There is a way to register types one by one and then retrieve all of them in the form of mpl::vector or similar. I've learned this trick on the boost mailing lists (perhaps from Dave Abrahams, although I can't recall for sure).
编辑:我从幻灯片28上 https://github.com/boostcon/2011_presentations/raw/master/thu/Boost .Generic.pdf 。
I learned it from slide 28 on https://github.com/boostcon/2011_presentations/raw/master/thu/Boost.Generic.pdf.
我不会在代码中使用MPL使其自我包含。
I won't use MPL in the code to make it self contained.
// The maximum number of types that can be registered with the same tag.
enum { kMaxRegisteredTypes = 10 };
template <int N>
struct Rank : Rank<N - 1> {};
template <>
struct Rank<0> {};
// Poor man's MPL vector.
template <class... Ts>
struct TypeList {
static const int size = sizeof...(Ts);
};
template <class List, class T>
struct Append;
template <class... Ts, class T>
struct Append<TypeList<Ts...>, T> {
typedef TypeList<Ts..., T> type;
};
template <class Tag>
TypeList<> GetTypes(Tag*, Rank<0>) { return {}; }
// Evaluates to TypeList of all types previously registered with
// REGISTER_TYPE macro with the same tag.
#define GET_REGISTERED_TYPES(Tag) \
decltype(GetTypes(static_cast<Tag*>(nullptr), Rank<kMaxRegisteredTypes>()))
// Appends Type to GET_REGISTERED_TYPES(Tag).
#define REGISTER_TYPE(Tag, Type) \
inline Append<GET_REGISTERED_TYPES(Tag), Type>::type \
GetTypes(Tag*, Rank<GET_REGISTERED_TYPES(Tag)::size + 1>) { \
return {}; \
} \
static_assert(true, "")
使用示例:
struct IntegralTypes;
struct FloatingPointTypes;
// Initially both type lists are empty.
static_assert(std::is_same<GET_REGISTERED_TYPES(IntegralTypes), TypeList<>>::value, "");
static_assert(std::is_same<GET_REGISTERED_TYPES(FloatingPointTypes), TypeList<>>::value, "");
// Add something to both lists.
REGISTER_TYPE(IntegralTypes, int);
REGISTER_TYPE(FloatingPointTypes, float);
static_assert(std::is_same<GET_REGISTERED_TYPES(IntegralTypes), TypeList<int>>::value, "");
static_assert(std::is_same<GET_REGISTERED_TYPES(FloatingPointTypes), TypeList<float>>::value, "");
// Add more types.
REGISTER_TYPE(IntegralTypes, long);
REGISTER_TYPE(FloatingPointTypes, double);
static_assert(std::is_same<GET_REGISTERED_TYPES(IntegralTypes), TypeList<int, long>>::value, "");
static_assert(std::is_same<GET_REGISTERED_TYPES(FloatingPointTypes), TypeList<float, double>>::value, "");
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