boost :: spirit :: x3属性兼容性规则，直觉还是代码？ [英] boost::spirit::x3 attribute compatibility rules, intuition or code?

问题描述

有什么地方描述了各种spirit :: x3规则定义操作如何影响属性兼容性？

我很惊讶于：

  x3 :: lexeme [x3 :: alpha> *（x3 :: alnum | x3 :: char _（'_'））] 
  

移动到融合适应的结构：

  struct Name {
 std :: string value; 
}; 
  

暂时，我摆脱了第一个强制性字母字符，但我仍然想表达一个定义名称字符串必须以字母开头的规则。是这种情况下，我需要尝试添加 eps ，直到它工作，或有一个陈述的原因，为什么上述不能工作？

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解决方案

如果这是写在某个地方， p>如果你不在开发中，你没有修复单元素序列适应性错误，所以是可能的。

由于属性变换/传播的一般性，有很多摆动的空间，但当然它只是记录，最终在代码中。换句话说：没有魔法。

在天气里，我会通过 qi :: as<> 或 qi :: attr_cast<> 。 X3没有它，但你可以使用一个规则来模仿它很容易：

Live on Coliru

  #include< iostream> 
 #include< boost / fusion / adapted / struct.hpp> 
 #include< boost / spirit / home / x3.hpp> 
 
命名空间x3 = boost :: spirit :: x3; 
 
 struct Name {
 std :: string value; 
}; 
 
 BOOST_FUSION_ADAPT_STRUCT（名称，值）
 
 int main（）{
 
 std :: string const input =Halleo123_1; 
名字
 
 bool ok = x3 :: parse（input.begin（），input.end（），
 x3 :: rule< struct _，std :: string> {} = 
 x3 :: alpha>> *（x3 :: alnum | x3 :: char _（'_'）），
 out）; 
 
 if（ok）
 std :: cout<< Parsed：<< out.value<< \\\
; 
 else 
 std :: cout<< 解析失败\\\
; 
} 
  

列印：

 已解析：Halleo123_1 
  

自动完成

因为X3使用c ++ 14核心语言功能很好，所以不难减少输入：

了解Boost.Spirit中的列表运算符（％）

Is there a document somewhere which describes how various spirit::x3 rule definition operations affect attribute compatibility?

I was surprised when:

x3::lexeme[ x3::alpha > *(x3::alnum | x3::char_('_')) ]

could not be moved into a fusion-adapted struct:

struct Name {
    std::string value;
};

For the time being, I got rid of the first mandatory alphabetical character, but I would still like to express a rule which defines that the name string must begin with a letter. Is this one of those situations where I need to try adding eps around until it works, or is there a stated reason why the above couldn't work?

I apologize if this has been written down somewhere, I couldn't find it.

解决方案

If you're not on the develop you don't have the fix for that single-element sequence adaptiation bug, so yeah it's probably that.

Due to the genericity of attribute transformation/propagation, there's a lot of wiggle room, but of course it's just documented and ultimately in the code. In other words: there's no magic.

In the Qi days I'd have "fixed" this by just spelling out the desired transform with qi::as<> or qi::attr_cast<>. X3 doesn't have it (yet), but you can use a rule to mimick it very easily:

Live On Coliru

#include <iostream>
#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/home/x3.hpp>

namespace x3 = boost::spirit::x3;

struct Name {
    std::string value;
};

BOOST_FUSION_ADAPT_STRUCT(Name, value)

int main() {

    std::string const input = "Halleo123_1";
    Name out;

    bool ok = x3::parse(input.begin(), input.end(),
            x3::rule<struct _, std::string>{} =
            x3::alpha >> *(x3::alnum | x3::char_('_')),
            out);

    if (ok)
        std::cout << "Parsed: " << out.value << "\n";
    else
        std::cout << "Parse failed\n";
}

Prints:

Parsed: Halleo123_1

Automate it

Because X3 works so nicely with c++14 core language features, it's not hard to reduce typing:

Understanding the List Operator (%) in Boost.Spirit

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