C++ C++；17使用std:：variant表示DOM
我试图学习如何使用C++17中的C++ C++；17使用std:：variant表示DOM,c++,dom,c++17,variant,C++,Dom,C++17,Variant,我试图学习如何使用C++17中的std:：variant。例如，我们开始使用它来表示DOM。尽管这项工作仍在进行中： 我想就std:：variant 还有一些关于编译器的输入支持 我有DOM表示代码（），它似乎可以很好地编译。但是，我看到相同的代码不能用编译 我想了解这种不兼容的原因是什么。还有，是否有人可以对“样式”发表评论，以及这是否是std:：variant的适当用法 #include <vector> #include <type_traits> #include
std:：variantstd:：variantDOM表示代码std:：variant#include <vector>
#include <type_traits>
#include <string>
#include <variant>
#include <unordered_map>
// https://dom.spec.whatwg.org/ : reference for the DOM.
namespace dragon {
namespace dom {
namespace traits_ns {
template <bool valid_node_type = false>
struct valid_node {
static constexpr bool value = valid_node_type;
};
template <typename T>
struct is_valid_node {
static constexpr bool value = std::is_base_of<valid_node<true>, T>::value && T::value;
};
// TODO: Need to define policy concepts which will check if the children
// of each node is of the right, allowed type.
}
struct Element;
struct Text;
struct Document;
struct Document_type;
struct Document_fragment;
struct Processing_instruction;
struct Comment;
using AttrList = std::vector<std::pair<std::string, std::string>>;
using AttrSet = std::unordered_map<std::string, std::string>;
using Node = std::variant<Document, Document_type, Document_fragment, Element, Text, Processing_instruction, Comment>;
using Children = std::vector<Node>;
struct Element final : traits_ns::valid_node<true> {
Element(std::string t, const Children& c, const AttrList& a) : tag{ t }, child{ c } {}
Element() = default;
~Element() = default;
std::string tag;
Children child;
AttrSet attr;
};
struct Text final : traits_ns::valid_node<true> {
explicit Text(std::string d) : data{ d } {}
std::string data;
};
struct Document final : traits_ns::valid_node<true> {
Document() = default;
~Document() = default;
};
struct Document_type final : traits_ns::valid_node<true> {};
struct Document_fragment final : traits_ns::valid_node<true> {};
struct Processing_instruction final : traits_ns::valid_node<true> {};
struct Comment final : traits_ns::valid_node<true> {};
} // namespace dom
} // namespace dragon
namespace dom = dragon::dom;
using std::vector;
int main()
{
dom::Node t{dom::Text{"Hello"}};
dom::Node e{dom::Element{"element", {}, {{"class", "blah"}}}};
return 0;
}
#包括
#包括
#包括
#包括
#包括
// https://dom.spec.whatwg.org/ ：DOM的引用。
名称空间龙{
名称空间dom{
名称空间特性{
模板
结构有效\u节点{
静态constexpr bool value=有效节点类型；
};
模板
结构是有效的节点{
静态constexpr bool value=std:：是：：value和&T：：value的基础；
};
//TODO:需要定义策略概念，以检查子项
//每个节点的类型都是正确的、允许的类型。
}
结构元素；
结构文本；
结构文档；
结构文档类型；
结构文档_片段；
结构处理指令；
结构注释；
使用AttrList=std:：vector；
使用AttrSet=std:：无序映射；
使用Node=std:：variant；
使用Children=std:：vector；
结构元素final:traits\u ns:：valid\u节点{
元素（std:：string t，const Children&c，const AttrList&a）：标记{t}，子{c}{
元素（）=默认值；
~Element（）=默认值；
std：：字符串标签；
儿童；
属性集属性；
};
结构文本final:traits\u ns:：valid\u节点{
显式文本（std:：string d）：数据{d}{
std：：字符串数据；
};
结构文档最终版本：traits\u ns:：valid\u节点{
Document（）=默认值；
~Document（）=默认值；
};
结构文档类型final:traits\u ns:：valid\u node{}；
结构文档\u片段final:traits\u ns:：valid\u node{}；
结构处理_指令final:traits_ns:：valid_node{}；
结构注释final:traits_ns:：valid_node{}；
}//名称空间dom
}//名称空间龙
名称空间dom=dragon:：dom；
使用std：：vector；
int main（）
{
dom:：Node t{dom:：Text{“Hello”}；
dom:：Node e{dom:：Element{“Element”，{}，{{{“class”，“blah”}}；
返回0；
}
#1 with x86-64 gcc (trunk)
In file included from /opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/move.h:55:0,
from /opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/stl_pair.h:59,
from /opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/stl_algobase.h:64,
from /opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/vector:60,
from <source>:1:
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/type_traits: In instantiation of 'struct std::is_trivially_destructible<dragon::dom::Document>':
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/type_traits:2859:25: required from 'constexpr const bool std::is_trivially_destructible_v<dragon::dom::Document>'
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:309:5: required from 'constexpr const bool std::__detail::__variant::_Traits<dragon::dom::Document, dragon::dom::Document_type, dragon::dom::Document_fragment, dragon::dom::Element, dragon::dom::Text, dragon::dom::Processing_instruction, dragon::dom::Comment>::_S_trivial_dtor'
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:317:20: required from 'constexpr const bool std::__detail::__variant::_Traits<dragon::dom::Document, dragon::dom::Document_type, dragon::dom::Document_fragment, dragon::dom::Element, dragon::dom::Text, dragon::dom::Processing_instruction, dragon::dom::Comment>::_S_trivial_move_assign'
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:642:16: required by substitution of 'template<class ... _Types> using _Move_assign_alias = std::__detail::__variant::_Move_assign_base<std::__detail::__variant::_Traits<_Types>::_S_trivial_move_assign, _Types ...> [with _Types = {dragon::dom::Document, dragon::dom::Document_type, dragon::dom::Document_fragment, dragon::dom::Element, dragon::dom::Text, dragon::dom::Processing_instruction, dragon::dom::Comment}]'
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:645:12: required from 'struct std::__detail::__variant::_Variant_base<dragon::dom::Document, dragon::dom::Document_type, dragon::dom::Document_fragment, dragon::dom::Element, dragon::dom::Text, dragon::dom::Processing_instruction, dragon::dom::Comment>'
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:1032:11: required from 'class std::variant<dragon::dom::Document, dragon::dom::Document_type, dragon::dom::Document_fragment, dragon::dom::Element, dragon::dom::Text, dragon::dom::Processing_instruction, dragon::dom::Comment>'
41 : <source>:41:86: required from here
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/type_traits:1285:12: error: invalid use of incomplete type 'struct dragon::dom::Document'
struct is_trivially_destructible
^~~~~~~~~~~~~~~~~~~~~~~~~
28 : <source>:28:10: note: forward declaration of 'struct dragon::dom::Document'
struct Document;
^~~~~~~~
In file included from /opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/move.h:55:0,
from /opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/stl_pair.h:59,
from /opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/stl_algobase.h:64,
from /opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/vector:60,
from <source>:1:
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/type_traits: In instantiation of 'constexpr const bool std::is_trivially_destructible_v<dragon::dom::Document>':
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:309:5: required from 'constexpr const bool std::__detail::__variant::_Traits<dragon::dom::Document, dragon::dom::Document_type, dragon::dom::Document_fragment, dragon::dom::Element, dragon::dom::Text, dragon::dom::Processing_instruction, dragon::dom::Comment>::_S_trivial_dtor'
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:317:20: required from 'constexpr const bool std::__detail::__variant::_Traits<dragon::dom::Document, dragon::dom::Document_type, dragon::dom::Document_fragment, dragon::dom::Element, dragon::dom::Text, dragon::dom::Processing_instruction, dragon::dom::Comment>::_S_trivial_move_assign'
<SNIP>
dragon::dom::Document_fragment, dragon::dom::Element, dragon::dom::Text, dragon::dom::Processing_instruction, dragon::dom::Comment}]' is implicitly deleted because the default definition would be ill-formed:
variant(const variant& __rhs) = default;
^~~~~~~
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:1087:7: error: use of deleted function 'constexpr std::_Enable_copy_move<false, false, false, false, _Tag>::_Enable_copy_move(const std::_Enable_copy_move<false, false, false, false, _Tag>&) [with _Tag = std::variant<dragon::dom::Document, dragon::dom::Document_type, dragon::dom::Document_fragment, dragon::dom::Element, dragon::dom::Text, dragon::dom::Processing_instruction, dragon::dom::Comment>]'
In file included from /opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:38:0,
from <source>:4:
/opt/compiler-explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/enable_special_members.h:301:15: note: declared here
constexpr _Enable_copy_move(_Enable_copy_move const&) noexcept = delete;
^~~~~~~~~~~~~~~~~
Compiler exited with result code 1
x86-64 gcc (trunk) (Editor #1, Compiler #1)
g++ (GCC-Explorer-Build) 8.0.0 20171009 (experimental)- cached
#1
在/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/move.h:55:0中包含的文件中，
来自/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/stl_pair.h:59，
来自/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/stl_algobase.h:64，
来自/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/vector:60，
发件人：1:
/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/type_traits:在“struct std:：is_minally_destructible”的实例化中：
/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/type_traits:2859:25:“constexpr const bool std:：is_minally_destructible_v”中必需的
/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:309:5:来自“constexpr const bool std:：”的必填项详细信息：：u变量：：_特征：：_S_平凡的_dtor'
/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:317:20:来自“constexpr const bool std:：”的必填项详细信息：：。。。。变量：：
/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:642:16:替换“使用移动分配别名=std的模板”时需要：：\uuuu详细信息：：\uu变量：：\uu移动分配分配基础[使用类型={dragon:：dom:：Document，dragon:：dom:：Document\u类型，dragon:：dom:：Document\u片段，dragon:：dom:：Element，dragon:：dom:：Text，dragon:：dom:：Processing\u指令，dragon:：dom:：Comment}'
/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:645:12:从“struct std:\ \详细信息：\ \变量：\ \变量\基础”中需要
/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:1032:11:必须来自“class std:：variant”
41:：41:86:从这里开始需要
/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/type_traits:1285:12:错误：无效使用不完整的类型“struct dragon:：dom:：Document”
结构是可破坏的
^~~~~~~~~~~~~~~~~~~~~~~~~
28:：28:10:注意：“struct dragon:：dom:：Document”的转发声明
结构文档；
^~~~~~~~
在/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/move.h:55:0中包含的文件中，
来自/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/stl_pair.h:59，
来自/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/bits/stl_algobase.h:64，
来自/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/vector:60，
发件人：1:
/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/type_traits:在“constexpr const bool std:：is_minally_destructible_v”的实例化中：
/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:309:5:来自“constexpr const bool std:：”的必填项详细信息：：u变量：：_特征：：_S_平凡的_dtor'
/opt/compiler explorer/gcc-trunk-20171009/include/c++/8.0.0/variant:317:20:来自“constexpr const bool std:：”的必填项详细信息：：。。。。变量：：
dragon:：dom:：Document_片段，dragon:：dom:：元素，dragon:：
#include <vector>
#include <type_traits>
#include <string>
#include <variant>
#include <unordered_map>
// https://dom.spec.whatwg.org/ : reference for the DOM.
namespace dragon {
namespace dom {
namespace traits_ns {
template <bool valid_node_type = false>
struct valid_node {
static constexpr bool value = valid_node_type;
};
template <typename T>
struct is_valid_node {
static constexpr bool value = std::is_base_of<valid_node<true>, T>::value && T::value;
};
// TODO: Need to define policy concepts which will check if the children
// of each node is of the right, allowed type.
}
struct Element;
struct Text;
struct Document;
struct Document_type;
struct Document_fragment;
struct Processing_instruction;
struct Comment;
using AttrList = std::vector<std::pair<std::string, std::string>>;
using AttrSet = std::unordered_map<std::string, std::string>;
using Node = std::variant<Document, Document_type, Document_fragment, Element, Text, Processing_instruction, Comment>;
using Children = std::vector<Node>;
struct Element final : traits_ns::valid_node<true> {
Element(std::string t, const Children& c, const AttrList& a);
Element() = default;
~Element() = default;
std::string tag;
Children child;
AttrSet attr;
};
struct Text final : traits_ns::valid_node<true> {
explicit Text(std::string d) : data{ d } {}
std::string data;
};
struct Document final : traits_ns::valid_node<true> {
Document() = default;
~Document() = default;
};
struct Document_type final : traits_ns::valid_node<true> {};
struct Document_fragment final : traits_ns::valid_node<true> {};
struct Processing_instruction final : traits_ns::valid_node<true> {};
struct Comment final : traits_ns::valid_node<true> {};
Element::Element(std::string t, const Children& c, const AttrList& a) : tag{ t }, child{ c } {}
} // namespace dom
} // namespace dragon
namespace dom = dragon::dom;
using std::vector;
int main()
{
dom::Node t{dom::Text{"Hello"}};
dom::Node e{dom::Element{"element", {}, {{"class", "blah"}}}};
return 0;
}