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将已分析序列的每个元素传递给返回规则属性类型的函数

boost-spirit-x3 boost-spirit c++17 css c++

rubenvb · 技术社区 · 6 年前

我想解析CSS颜色函数(为了简单起见,所有参数都是0到255之间的数字)

rgb(r,g,b)
rgba(r,g,b,a)
hsl(h,s,l)
hsla(h,s,l,a)

进入之内

struct color
{
    color(std::uint8_t r, std::uint8_t g, std::uint8_t b, std::uint8_t a) : red{r}, green{g}, blue{b}, alpha{a} {}
    static color hsl(std::uint8_t h, std::uint8_t s, std::uint8_t l, std::uint8_t a) { ... }
    std::uint8_t red;
    std::uint8_t green;
    std::uint8_t blue;
    std::uint8_t alpha;
}

我有工作 hsl 将h、s和l转换为rgb值的函数实现。

我也有 rule s处理前两个功能:

constexpr auto uint8 = uint_parser<std::uint8_t>{};
const auto color_rgb = rule<struct rgb, color>{"rgb"}
                     = lit("rgb") >> '(' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> ')' >> attr(255);
const auto color_rgba = rule<struct rgba, color>{"rgba"}
                      = lit("rgba") >> '(' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> ')';

因为我用过

BOOST_FUSION_ADAPT_STRUCT(color,
                          red, green, blue, alpha)

问题在于 高速铁路 功能。我一秒钟也做不到 BOOST_FUSION_ADAPT_STRUCT 因此,我考虑在相应的值序列上使用语义操作,其中语义操作将简单地构造 color 从序列中。像这样:

const auto color_hsl = rule<struct hsl, color, true>{"hsl"}
                   = (lit("hsl") >> '(' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> ')' >> attr(255))[color::hsl];

这不管用,否则我就不会问这个问题了。boost.spirit.x3也没有

[ qi::_val = phx::construct<color>(...), qi::_1, qi::_2, qi::_3, qi::_4) ];

我好像想手动做什么 增强融合适应结构 是的,但在语义操作中。这可能吗?我应该如何处理?我知道序列的属性应该是一个具有四个解析值的“融合向量”类元组实体。我想把它们提取出来塞进 color::hsl 生成规则的属性。

1 回复 | 直到 6 年前

sehe 6 年前

这里有很多提示。

我不能再做一次增强融合适应结构

当然可以,看吧 BOOST_FUSION_ADAPT_STRUCT_NAMED
在QI中,这一一般形式似乎适用:
```
[ qi::_val = phxfunction(qi::_0) ]
```
你可以通过让你自己的演员类型进一步简化,这样你就可以提供你的“工厂行动”: [ factory(&Foo::makeBar) ] .

如果您将 fusion::apply _你可以避免使用人工融合序列。
但是,您可能希望了解语义操作的这个非常好的隐藏属性兼容模式: BOOST_SPIRIT_ACTIONS_ALLOW_ATTR_COMPAT .隐藏在那个变更日志中:

语义操作现在支持属性兼容性。这是一个突破性的变化,但定义 提升精神行动允许同胞 必须定义新行为才能启动。 默认情况下,旧行为仍然存在 .

你可以用更少的调整来获得你想要的行为。

X3真的很有延展性。我们可以吃那个 factory 上面所描述的助手包括:

auto factory = [](auto f) {
    return [f](auto& ctx) {
        x3::_val(ctx) = my_apply(f, x3::_attr(ctx));
    };
};

我马上就把 my_apply (对于 boost::fusion::apply 如前所述):

namespace detail {
    template <class F, class Sequence, std::size_t... I>
        constexpr decltype(auto) apply_impl(F&& f, Sequence&& t, std::index_sequence<I...>)
        {
            return std::invoke(std::forward<F>(f), boost::fusion::at_c<I>(std::forward<Sequence>(t))...);
        }
}

template <class F, class Sequence>
    constexpr decltype(auto) my_apply(F&& f, Sequence&& t)
    {
        return detail::apply_impl(
                std::forward<F>(f), std::forward<Sequence>(t),
                std::make_index_sequence<typename boost::fusion::result_of::size<std::remove_reference_t<Sequence> >::type{}>{});
    }

现在我们可以让解析器:

namespace parser {
    using namespace x3;

    constexpr auto uint8  = uint_parser<std::uint8_t>{};

    auto factory = [](auto f) {
        return [f](auto& ctx) {
            x3::_val(ctx) = my_apply(f, x3::_attr(ctx));
        };
    };

    const auto color_rgb  = rule<struct rgb, ast::color>{"rgb"}
                          = lit("rgb") >> '(' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> x3::attr(255u) >> ')';
    const auto color_rgba = rule<struct rgba, ast::color>{"rgba"}
                          = lit("rgba") >> '(' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> ')';
    const auto color_hsl  = rule<struct hsl, ast::color>{"hsl"}
                          = (lit("hsl") >> '(' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> attr(255u) >> ')') [factory(ast::color::hsl)];

    const auto color = skip(space) [ color_rgba | color_rgb | color_hsl ];
}

并用以下方法进行测试:

int main() {
    for (std::string const input : {
            "rgb(1,2,3)",
            "rgba(4,5,6,7)",
            "hsl(8,9,10)" }) 
    {
        std::cout << " ----- Parsng " << std::quoted(input) << " --------\n";
        auto begin = input.begin(), end = input.end();

        ast::color result;
        bool success = parse(begin, end, parser::color, result);

        if (success) {
            std::cout << "parsed: ";
            std::cout << result << "\n";
        } else {
            std::cout << "failed\n";
        }

        if (begin != end) {
            std::cout << "Remaining unparsed: " << std::quoted(std::string(begin, end)) << std::endl;
        }
    }
}

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 ----- Parsng "rgb(1,2,3)" --------
parsed: rgba(1,2,3,255)
 ----- Parsng "rgba(4,5,6,7)" --------
parsed: rgba(4,5,6,7)
 ----- Parsng "hsl(8,9,10)" --------
TODO: implement static ast::color ast::color::hsl(uint8_t, uint8_t, uint8_t, uint8_t)(8,9,10,255)
parsed: rgba(8,9,10,255)

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

namespace x3 = boost::spirit::x3;


namespace ast {
    using std::uint8_t;

    struct color {
        uint8_t red, green, blue, alpha;

        color(uint8_t r=0, uint8_t g=0, uint8_t b=0, uint8_t a=255) : red{r}, green{g}, blue{b}, alpha{a} {}

        static color hsl(uint8_t h, uint8_t s, uint8_t l, uint8_t a) { 
            std::cerr << "TODO: implement " << __PRETTY_FUNCTION__ << "(" << 1*h << "," << 1*s << "," << 1*l << "," << 1*a << ")\n";
            return {h,s,l,a}; }
    };

    static inline std::ostream& operator<<(std::ostream& os, color const& c) {
        return os << "rgba(" << 1*c.red << "," << 1*c.green << "," << 1*c.blue << "," << 1*c.alpha << ")";
    }
}

BOOST_FUSION_ADAPT_STRUCT(ast::color, red, green, blue, alpha);

namespace {
    namespace detail {
        template <class F, class Sequence, std::size_t... I>
            constexpr decltype(auto) apply_impl(F&& f, Sequence&& t, std::index_sequence<I...>)
            {
                return std::invoke(std::forward<F>(f), boost::fusion::at_c<I>(std::forward<Sequence>(t))...);
            }
    }

    template <class F, class Sequence>
        constexpr decltype(auto) my_apply(F&& f, Sequence&& t)
        {
            return detail::apply_impl(
                    std::forward<F>(f), std::forward<Sequence>(t),
                    std::make_index_sequence<typename boost::fusion::result_of::size<std::remove_reference_t<Sequence> >::type{}>{});
        }
}

namespace parser {
    using namespace x3;

    constexpr auto uint8  = uint_parser<std::uint8_t>{};

    auto factory = [](auto f) {
        return [f](auto& ctx) {
            x3::_val(ctx) = my_apply(f, x3::_attr(ctx));
        };
    };

    const auto color_rgb  = rule<struct rgb, ast::color>{"rgb"}
                          = lit("rgb") >> '(' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> x3::attr(255u) >> ')';
    const auto color_rgba = rule<struct rgba, ast::color>{"rgba"}
                          = lit("rgba") >> '(' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> ')';
    const auto color_hsl  = rule<struct hsl, ast::color>{"hsl"}
                          = (lit("hsl") >> '(' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> attr(255u) >> ')') [factory(ast::color::hsl)];

    const auto color = skip(space) [ color_rgba | color_rgb | color_hsl ];
} 

int main() {
    for (std::string const input : {
            "rgb(1,2,3)",
            "rgba(4,5,6,7)",
            "hsl(8,9,10)" }) 
    {
        std::cout << " ----- Parsng " << std::quoted(input) << " --------\n";
        auto begin = input.begin(), end = input.end();

        ast::color result;
        bool success = parse(begin, end, parser::color, result);

        if (success) {
            std::cout << "parsed: ";
            std::cout << result << "\n";
        } else {
            std::cout << "failed\n";
        }

        if (begin != end) {
            std::cout << "Remaining unparsed: " << std::quoted(std::string(begin, end)) << std::endl;
        }
    }
}

它似乎不存在。当然你可以复制到 std::tuple 使用 std::apply (也) experimental )