标签：boost-spirit-x3 c css c17 boost-spirit
我想解析CSS颜色函数(为简单起见,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)
成
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;
}
我有一个工作的hsl函数实现,它将h,s和l转换为rgb值.
我也有处理前两个函数的规则：
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 >> ')';
这是因为我使用过
BOOST_FUSION_ADAPT_STRUCT(color,
red, green, blue, alpha)
问题在于hsl函数.我不能做第二个BOOST_FUSION_ADAPT_STRUCT,所以我想到对各个值序列使用语义动作,其中语义动作将简单地从序列构造颜色.像这样的东西：
const auto color_hsl = rule<struct hsl, color, true>{"hsl"}
= (lit("hsl") >> '(' >> uint8 >> ',' >> uint8 >> ',' >> uint8 >> ')' >> attr(255))[color::hsl];
这不起作用,或者我不会问这个问题. Boost.Spirit.X3也没有任何意义上的东西
[ qi::_val = phx::construct<color>(...), qi::_1, qi::_2, qi::_3, qi::_4) ];
似乎我想手动执行BOOST_FUSION_ADAPT_STRUCT所执行的操作,但是在语义操作中.这是可能的,我应该如何处理？我知道序列的属性应该是具有四个解析值的“融合矢量”元组类实体.我想提取它们并将它们填充到color :: hsl中以生成规则的属性.
解决方法:
这里有许多提示.
>
I cannot do a second BOOST_FUSION_ADAPT_STRUCT
当然可以,见BOOST_FUSION_ADAPT_STRUCT_NAMED
>在齐这种一般形式似乎适用：
[ qi::_val = phxfunction(qi::_0) ]
你可以通过制作你自己的演员类型来进一步简化它,这样你就可以提供你的“工厂动作”：[factory(& Foo :: makeBar)].
如果你投入fusion ::apply¹的实现,你可以避免处理Fusion序列manuallt
>但是,您可能想要了解这个 – 非常隐蔽 – 语义操作的属性兼容模式：BOOST_SPIRIT_ACTIONS_ALLOW_ATTR_COMPAT.隐藏在该更改日志中：
Semantic actions now support attribute compatibility. This is a breaking change but #define
BOOST_SPIRIT_ACTIONS_ALLOW_ATTR_COMPATmust be defined in order for the new behavior to kick in. By default, the old behavior is still in place.
你可以通过更少的调整来获得你想要的行为.
> X3真的具有可塑性.我们可以将上面描述的工厂助手尽可能地：
auto factory = [](auto f) {
return [f](auto& ctx) {
x3::_val(ctx) = my_apply(f, x3::_attr(ctx));
};
};
我将抛出my_apply的快速草稿(对于前面描述的boost :: fusion :: apply)：
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{}>{});
}
现在我们可以拥有解析器：
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 ];
}
并测试它：
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;
}
}
}
打印：
----- 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)
完整清单
#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;
}
}
}
¹似乎不存在.当然你可以复制到std :: tuple并使用std::apply(也是experimental)
标签：boost-spirit-x3,c,css,c17,boost-spirit 来源： https://codeday.me/bug/20190827/1745675.html
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