Boost Spirit x3:解析为结构体-C/C++问题

Boost Spirit x3: parse into structs(Boost Spirit x3:解析为结构体)

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问题描述

来自 Boost Spirit X3 教程:

From the Boost Spirit X3 tutorial:

首先，让我们创建一个代表员工的结构体:

First, let's create a struct representing an employee:

namespace client { namespace ast
{
   struct employee
   {
       int age;
       std::string surname;
       std::string forename;
       double salary;
   };
}}

然后，我们需要将我们的员工结构告诉 Boost.Fusion 以使其成为语法可以利用的一流融合公民.

Then, we need to tell Boost.Fusion about our employee struct to make it a first-class fusion citizen that the grammar can utilize.

BOOST_FUSION_ADAPT_STRUCT(
    client::ast::employee,
    (int, age)
    (std::string, surname)
    (std::string, forename)
    (double, salary)
)`

[...]在fusion 看来，结构体只是元组的一种形式.你可以适应任何struct 是一个完全符合的融合元组.[...]应用我们上面的折叠规则，RHS 具有以下属性:fusion::vector结构员工与融合::矢量.所以，start 的 RHS 就地使用了 start 的属性(一个结构体员工)当它开始工作时.

[...] In fusion's view, a struct is just a form of a tuple. You can adapt any struct to be a fully conforming fusion tuple. [...] Applying our collapsing rules above, the RHS has an attribute of: fusion::vector<int, std::string, std::string, double> The struct employee IS compatible with fusion::vector. So, the RHS of start uses start's attribute (a struct employee) in-situ when it does its work.

如果我很好理解，这个逻辑在很大程度上依赖于属性的顺序.

If I well understood, this logic heavily relies on the order of the attributes.

现在，我需要解析类似的东西

Now, I am in a situation where I need to parse something like

Layer "L1" {
    number = 23
    color = green
    visible = true
}

结构化

struct LayerInfo
{
    std::string layerName;
    int layerNumber;
    std::string color;
    bool visible;
}

问题是，图层属性的顺序可以改变，这与上面看到的逻辑相反.

The problem is, the order of the layer properties can change, which is in opposition with the logic seen above.

解析这样的结构的正确方法是什么?我是否一定需要使用语义动作?

Which is the correct way to parse into a struct like this? Do I need necessarily need to use semantic actions?

推荐答案

我喜欢@llonesmiz 在评论中的方法.

I love @llonesmiz's approach in the comment.

不过，我不得不"尝试使用 X3 的我最喜欢的方法，也使用函数组合.这是解析和传播值的方法的草图.

I "had to" try my favorite approach with X3 using functional composition too, though. Here's a sketch of the approach which does parse and propagate the values.

缺少对属性存在/唯一性的检查.(我认为这样的事情可以使用 x3::with<> 上下文添加来实现，它基本上包含一个 std::set<VT::*>.当然，这样的事情需要(依赖于实现?)强制转换或擦除包装器).

Missing are checks on property presence/uniqueness. (I think such a thing is doable using a x3::with<> context addition that basically contains a std::set<V T::*>. Of course such a thing needs (implementation dependent?) casts or an erasure wrapper).

暂时不加评论:

生活在 Coliru

#include <iostream> //#define BOOST_SPIRIT_X3_DEBUG #include <boost/spirit/home/x3.hpp> #include <boost/fusion/include/adapt_struct.hpp> #include <boost/fusion/include/io.hpp> struct LayerInfo { std::string layerName; int layerNumber = 0; std::string color; bool visible = false; }; namespace Parser { namespace x3 = boost::spirit::x3; // custom type parsers auto quoted = rule<std::string>("quoted", x3::lexeme [ '"' >> *('\' >> x3::char_ | ~x3::char_('"')) >> '"' ]); struct colors_type : x3::symbols<char> { colors_type() { this->add("red")("blue")("green")("black"); } } static const colors; namespace detail { template <typename T> auto propagate(T member) { return [=](auto& ctx){ x3::traits::move_to(x3::_attr(ctx), x3::_val(ctx).*member); }; } template <typename T> auto make_member_parser(int T::* const member) { return x3::int_ [propagate(member)]; } template <typename T> auto make_member_parser(bool T::* const member) { return x3::bool_ [propagate(member)]; } template <typename T> auto make_member_parser(std::string T::* const member) { return x3::raw[colors] [propagate(member)]; } template <typename T = LayerInfo, typename P> auto rule(const char* debug, P p) { return x3::rule<struct _, T> {debug} = x3::skip(x3::space)[p]; }; auto property = [](auto label, auto member) { return rule(label, x3::as_parser(label) >> '=' >> make_member_parser(member)); }; } using detail::rule; using detail::propagate; using detail::property; auto name = rule("name", "Layer" >> quoted [propagate(&LayerInfo::layerName)]); auto number = property("number", &LayerInfo::layerNumber); auto color = property("color", &LayerInfo::color); auto visible = property("visible", &LayerInfo::visible); auto layer_info = name >> '{' >> +(number | color | visible) >> '}'; auto grammar = rule("layer_info", layer_info); } std::ostream& operator<<(std::ostream& os, LayerInfo const& li) { return os << "LayerInfo "" << li.layerName << ""{" << "number=" << li.layerNumber << " " << "color=" << li.color << " " << "visible=" << std::boolalpha << li.visible << "} "; } int main() { std::string const sample = R"(Layer "L1" { number = 23 color = green visible = true })"; LayerInfo v; auto f = sample.begin(), l = sample.end(); bool ok = parse(f, l, Parser::grammar, v); if (ok) std::cout << "Parsed: " << v << " "; else std::cout << "Parse failed "; if (f!=l) std::cout << "Remaining unparsed: '" << std::string(f,l) << "' "; }

印刷品

Parsed: LayerInfo "L1"{number=23 color=green visible=true}

机智调试信息:生活在 Coliru

<layer_info> <try>Layer "L1" { num</try> <name> <try>Layer "L1" { num</try> <quoted> <try> "L1" { number =</try> <success> { number = 23 </success> <attributes>[L, 1]</attributes> </quoted> <success> { number = 23 </success> <attributes>LayerInfo "L1"{number=0 color= visible=false} </attributes> </name> <number> <try> number = 23 </try> <success> color = green </success> <attributes>LayerInfo "L1"{number=23 color= visible=false} </attributes> </number> <number> <try> color = green </try> <fail/> </number> <color> <try> color = green </try> <success> visible = true </success> <attributes>LayerInfo "L1"{number=23 color=green visible=false} </attributes> </color> <number> <try> visible = true </try> <fail/> </number> <color> <try> visible = true </try> <fail/> </color> <visible> <try> visible = true </try> <success> }</success> <attributes>LayerInfo "L1"{number=23 color=green visible=true} </attributes> </visible> <number> <try> }</try> <fail/> </number> <color> <try> }</try> <fail/> </color> <visible> <try> }</try> <fail/> </visible> <success></success> <attributes>LayerInfo "L1"{number=23 color=green visible=true} </attributes> </layer_info>

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