问题描述
我正在尝试解析以下结构:
I am trying to parse the following struct:
struct Selector {
std::string element;
std::string id;
std::vector<std::string> classes;
};
此结构用于解析形式为 element#id.class1.class2.classn 的选择器.这些选择器始终以1或不包含任何元素开头，可以包含1或不包含id，并且可以包含0到n个类.
This struct is used to parse selectors in the form element#id.class1.class2.classn. These selectors always start with 1 or no elements, could contain 1 or no ids, and could contain 0 to n classes.
这会变得更加复杂，因为类和id可以以任何顺序出现，因此以下选择器都是有效的: element#id.class1 ， .class1#id.class2.class3 ，#id.class1.class2 ， .class1.class2#id .因此，我无法使用，而且我也无法使用 BOOST_FUSION_ADAPT_STRUCT .
This gets even more complicated though, because classes and id can appear in any order, so the following selectors are all valid: element#id.class1, .class1#id.class2.class3, #id.class1.class2, .class1.class2#id. For this reason, I have not been able to use hold[], or at<T>() approaches described here, and I also have not been able to use BOOST_FUSION_ADAPT_STRUCT.
我能够合成此结构的唯一方法是遵循以下规则:
The only way that I have been able to synthesize this struct, is with the following rules:
auto element = [](auto& ctx){x3::_val(ctx).element = x3::_attr(ctx);};
auto id = [](auto& ctx){x3::_val(ctx).id = x3::_attr(ctx);};
auto empty = [](auto& ctx){x3::_val(ctx) = "";};
auto classes = [](auto& ctx){x3::_val(ctx).classes.insert(x3::_val(ctx).classes.end(), x3::_attr(ctx).begin(), x3::_attr(ctx).end());};
auto elementRule = x3::rule<class EmptyIdClass, std::string>() = +x3::char_("a-zA-Z") | x3::attr("");
auto idRule = x3::rule<class EmptyIdClass, std::string>() = ("#" >> +x3::char_("a-zA-Z")) | x3::attr("");
auto classesRule = x3::rule<class ClassesClass, std::vector<std::string>>() = *("." >> +x3::char_("a-zA-Z"));
auto selectorRule = x3::rule<class TestClass, Selector>() = elementRule[element] >> classesRule[classes] >> idRule[id] >> classesRule[classes];
解析此结构的最佳方法是什么?是否可以使用 BOOST_FUSION_ADAPT_STRUCT 自然地合成此选择器结构，而无需语义动作?
What would be the best way to parse this struct? Is it possible to synthesize this selector struct naturally, using BOOST_FUSION_ADAPT_STRUCT, and without semantic actions?
似乎每次我觉得我都能够抓住Spirit X3的诀窍时，我偶然遇到了一个新挑战.在这种情况下，我了解了回溯的问题，有关使用 at< T>() 此处，并且我还了解到X3不支持 hold [] .
It seems like everytime I think I am am getting the hang of Spirit X3, I stumble upon a new challenge. In this particular case, I learned about issues with backtracking, about an issue with using at<T>() that was introduced in Boost 1.70 here, and I also learned that hold[] is not supported by X3.
推荐答案
我之前写过类似的答案:
I've written similar answers before:
- 使用Boost.Spirit X3解析CSS (a力求在Qi和X3中更完整地解析CSS)
- 使用boost :: spirit进行解析以任何顺序命名的参数(注释中为Qi和X3)
- Boost Spirit x3:解析为结构
- 在运行时合并规则并返回规则
- Parsing CSS with Boost.Spirit X3 (a treasure trove for more complete CSS parsing in both Qi and X3)
- Using boost::spirit to parse named parameters in any order (Qi and X3 in the comments)
- Boost Spirit x3: parse into structs
- Combining rules at runtime and returning rules
我认为您不能直接进行融合调整.尽管如果您很有动力(例如，您已经有适应的结构)，您可以 从中获得一些通用的帮助.
I don't think you can directly fusion-adapt. Although if you are very motivated (e.g. you already have the adapted structs) you could make some generic helpers off that.
说句公道话，对我的代码来说，对代码进行一点重组似乎已经很不错了.这是我努力使其更优雅/更方便的方法.我将像BOOST_FUSION_ADAPT_XXX一样介绍一个辅助宏，但不需要任何Boost Fusion.
To be fair, a little bit of restructuring in your code seems pretty nice to me, already. Here's my effort to make it more elegant/convenient. I'll introduce a helper macro just like BOOST_FUSION_ADAPT_XXX, but not requiring any Boost Fusion.
和往常一样，我喜欢从基础开始.理解目标是成功的一半:
As always, I like to start with the basics. Understanding the goal is half the battle:
namespace Ast {
using boost::optional;
struct Selector {
// These selectors always
// - start with 1 or no elements,
// - could contain 1 or no ids, and
// - could contain 0 to n classes.
optional<std::string> element;
optional<std::string> id;
std::vector<std::string> classes;
friend std::ostream& operator<<(std::ostream& os, Selector const&s) {
if (s.element.has_value()) os << s.element.value();
if (s.id.has_value()) os << "#" << s.id.value();
for (auto& c : s.classes) os << "." << c;
return os;
}
};
}
请注意，我固定了某些部分的可选性以反映现实生活.
Note that I fixed the optionality of some parts to reflect real life.
魔术酱(见下文)
#include "propagate.hpp"
DEF_PROPAGATOR(Selector, id, element, classes)
我们稍后将对此进行深入研究.可以说它生成了您必须繁琐地编写的语义动作.
We'll dig into this later. Suffice it to say it generates the semantic actions that you had to tediously write.
现在，我们可以大大简化解析器规则，并运行测试:
Now, we can simplify the parser rules a lot, and run the tests:
int main() {
auto name = as<std::string>[x3::alpha >> *x3::alnum];
auto idRule = "#" >> name;
auto classesRule = +("." >> name);
auto selectorRule
= x3::rule<class TestClass, Ast::Selector>{"selectorRule"}
= +( name [ Selector.element ]
| idRule [ Selector.id ]
| classesRule [ Selector.classes ]
)
;
for (std::string const& input : {
"element#id.class1.class2.classn",
"element#id.class1",
".class1#id.class2.class3",
"#id.class1.class2",
".class1.class2#id",
})
{
Ast::Selector sel;
std::cout << std::quoted(input) << " -->\n";
if (x3::parse(begin(input), end(input), selectorRule >> x3::eoi, sel)) {
std::cout << "\tSuccess: " << sel << "\n";
} else {
std::cout << "\tFailed\n";
}
}
}
查看 在魔盒上直播" ，打印:
See it Live On Wandbox, printing:
"element#id.class1.class2.classn" -->
Success: element#id.class1.class2.classn
"element#id.class1" -->
Success: element#id.class1
".class1#id.class2.class3" -->
Success: #id.class1.class2.class3
"#id.class1.class2" -->
Success: #id.class1.class2
".class1.class2#id" -->
Success: #id.class1.class2
魔术
现在，我如何生成这些动作?使用一点Boost预处理器:
The Magic
Now, how did I generate those actions? Using a little bit of Boost Preprocessor:
#define MEM_PROPAGATOR(_, T, member) \
Propagators::Prop<decltype(std::mem_fn(&T::member))> member { std::mem_fn(&T::member) };
#define DEF_PROPAGATOR(type, ...) \
struct type##S { \
using T = Ast::type; \
BOOST_PP_SEQ_FOR_EACH(MEM_PROPAGATOR, T, BOOST_PP_VARIADIC_TO_SEQ(__VA_ARGS__)) \
} static const type {};
现在，您可能会看到它定义了名为AST类型的静态const变量.
Now, you might see that it defines static const variables named like the Ast types.
真正的魔力是 Propagators :: Prop< F> ，它具有一些分配功能，可以容纳容器属性和成员.否则，它将中继到 x3 :: traits :: move_to :
The real magic is Propagators::Prop<F> which has a bit of dispatch to allow for container attributes and members. Otherwise it just relays to x3::traits::move_to:
namespace Propagators {
template <typename F>
struct Prop {
F f;
template <typename Ctx>
auto operator()(Ctx& ctx) const {
return dispatch(x3::_attr(ctx), f(x3::_val(ctx)));
}
private:
template <typename Attr, typename Dest>
static inline void dispatch(Attr& attr, Dest& dest) {
call(attr, dest, is_container(attr), is_container(dest));
}
template <typename T>
static auto is_container(T const&) { return x3::traits::is_container<T>{}; }
static auto is_container(std::string const&) { return boost::mpl::false_{}; }
// tags for dispatch
using attr_is_container = boost::mpl::true_;
using attr_is_scalar = boost::mpl::false_;
using dest_is_container = boost::mpl::true_;
using dest_is_scalar = boost::mpl::false_;
template <typename Attr, typename Dest>
static inline void call(Attr& attr, Dest& dest, attr_is_scalar, dest_is_scalar) {
x3::traits::move_to(attr, dest);
}
template <typename Attr, typename Dest>
static inline void call(Attr& attr, Dest& dest, attr_is_scalar, dest_is_container) {
dest.insert(dest.end(), attr);
}
template <typename Attr, typename Dest>
static inline void call(Attr& attr, Dest& dest, attr_is_container, dest_is_container) {
dest.insert(dest.end(), attr.begin(), attr.end());
}
};
}
奖金
传播器类型的许多复杂性来自处理容器属性.但是，您实际上不需要任何这些内容:
BONUS
A lot of the complexity in the propagator type is from handling container attributes. However, you don't actually need any of that:
auto name = as<std::string>[x3::alpha >> *x3::alnum];
auto selectorRule
= x3::rule<class selector_, Ast::Selector>{"selectorRule"}
= +( name [ Selector.element ]
| '#' >> name [ Selector.id ]
| '.' >> name [ Selector.classes ]
)
;
绰绰有余，并且可以将传播帮助器简化为:
Is more than enough, and the propagation helper can be simplified to:
namespace Propagators {
template <typename F> struct Prop {
F f;
template <typename Ctx>
auto operator()(Ctx& ctx) const {
return call(x3::_attr(ctx), f(x3::_val(ctx)));
}
private:
template <typename Attr, typename Dest>
static inline void call(Attr& attr, Dest& dest) {
x3::traits::move_to(attr, dest);
}
template <typename Attr, typename Elem>
static inline void call(Attr& attr, std::vector<Elem>& dest) {
dest.insert(dest.end(), attr);
}
};
}
如您所见，蒸发标记分发具有有益的作用.
As you can see evaporating the tag dispatch has a beneficial effect.
再次参见简化版本 在魔盒上直播 .
See the simplified version Live On Wandbox again.
对于此网站上的后代:
-
test.cpp
test.cpp
//#define BOOST_SPIRIT_X3_DEBUG
#include <boost/spirit/home/x3.hpp>
#include <iostream>
#include <iomanip>
namespace x3 = boost::spirit::x3;
namespace Ast {
using boost::optional;
struct Selector {
// These selectors always
// - start with 1 or no elements,
// - could contain 1 or no ids, and
// - could contain 0 to n classes.
optional<std::string> element;
optional<std::string> id;
std::vector<std::string> classes;
friend std::ostream& operator<<(std::ostream& os, Selector const&s) {
if (s.element.has_value()) os << s.element.value();
if (s.id.has_value()) os << "#" << s.id.value();
for (auto& c : s.classes) os << "." << c;
return os;
}
};
}
#include "propagate.hpp"
DEF_PROPAGATOR(Selector, id, element, classes)
#include "as.hpp"
int main() {
auto name = as<std::string>[x3::alpha >> *x3::alnum];
auto selectorRule
= x3::rule<class selector_, Ast::Selector>{"selectorRule"}
= +( name [ Selector.element ]
| '#' >> name [ Selector.id ]
| '.' >> name [ Selector.classes ]
)
;
for (std::string const& input : {
"element#id.class1.class2.classn",
"element#id.class1",
".class1#id.class2.class3",
"#id.class1.class2",
".class1.class2#id",
})
{
Ast::Selector sel;
std::cout << std::quoted(input) << " -->\n";
if (x3::parse(begin(input), end(input), selectorRule >> x3::eoi, sel)) {
std::cout << "\tSuccess: " << sel << "\n";
} else {
std::cout << "\tFailed\n";
}
}
}
propagate.hpp
propagate.hpp
#pragma once
#include <boost/preprocessor/cat.hpp>
#include <boost/preprocessor/seq/for_each.hpp>
#include <functional>
namespace Propagators {
template <typename F> struct Prop {
F f;
template <typename Ctx>
auto operator()(Ctx& ctx) const {
return call(x3::_attr(ctx), f(x3::_val(ctx)));
}
private:
template <typename Attr, typename Dest>
static inline void call(Attr& attr, Dest& dest) {
x3::traits::move_to(attr, dest);
}
template <typename Attr, typename Elem>
static inline void call(Attr& attr, std::vector<Elem>& dest) {
dest.insert(dest.end(), attr);
}
};
}
#define MEM_PROPAGATOR(_, T, member) \
Propagators::Prop<decltype(std::mem_fn(&T::member))> member { std::mem_fn(&T::member) };
#define DEF_PROPAGATOR(type, ...) \
struct type##S { \
using T = Ast::type; \
BOOST_PP_SEQ_FOR_EACH(MEM_PROPAGATOR, T, BOOST_PP_VARIADIC_TO_SEQ(__VA_ARGS__)) \
} static const type {};
as.hpp
as.hpp
#pragma once
#include <boost/spirit/home/x3.hpp>
namespace {
template <typename T>
struct as_type {
template <typename...> struct tag{};
template <typename P>
auto operator[](P p) const {
return boost::spirit::x3::rule<tag<T,P>, T> {"as"}
= p;
}
};
template <typename T>
static inline const as_type<T> as = {};
}
这篇关于使用Boost Spirit X3解析具有交替标记的Selector结构的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！