Question

尝试在REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE jupyterhub/jupyterhub latest 3726912b8cfc 5 months ago 811.5 MB <none> <none> 7cdb3c49d61f 2 years ago 4.766 GB中存储boost::recursive_variant_type对象时遇到问题。

让我们假设以下代码并假定包含所有必需的头文件：

header.h

boost::unordered_map

source.cpp

// [...]
namespace example_namespace 
{

using my_custom_class_t = boost::make_recursive_variant<
        bool,
        double,
        std::string,
        std::vector<boost::recursive_variant_>,
        boost::unordered_map<std::string, boost::recursive_variant_>
    >::type;

using my_custom_map = boost::unordered_map<std::string, my_custom_class_t>;

std::vector<my_custom_map> stack_;

}

只要我不使用// [...] namespace example_namespace { std::pair<std::string, my_custom_class_t> my_pair { "hi", my_custom_class_t(true) }; std::string s = my_pair.first; my_custom_class_t t = my_pair.second; // here comes the bad part my_custom_map my_map; my_map.emplace(s, t); // <- this is where compilation aborts stack_.emplace_back(my_map); }类（“最糟糕的地方”行上方的所有内容），代码就可以正常编译，但是一旦我要将递归变量类型存储在地图中（例如boost::unordered_map<std::string, my_custom_class_t>），编译器将引发以下错误：

my_map

是否有可能由于某些原因而无法将递归变体（例如就内存分配而言）存储在1>c:\...\include\xhash(31): error C2440: 'type cast': cannot convert from 'const _Kty' to 'size_t' 1> with 1> [ 1> _Kty=std::string 1> ] 1>c:\...\include\xhash(31): note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called 1>d:\...\boost\container_hash\extensions.hpp(358): note: see reference to function template instantiation 'size_t stdext::hash_value<T>(const _Kty &)' being compiled 1> with 1> [ 1> T=std::string, 1> _Kty=std::string 1> ] 1>d:\...\boost\container_hash\extensions.hpp(357): note: while compiling class template member function 'size_t boost::hash<K>::operator ()(const T &) const' 1> with 1> [ 1> K=std::string, 1> T=std::string 1> ] 1>d:\...\boost\unordered\detail\implementation.hpp(2623): note: see reference to function template instantiation 'size_t boost::hash<K>::operator ()(const T &) const' being compiled 1> with 1> [ 1> K=std::string, 1> T=std::string 1> ] 1>d:\...\boost\type_traits\is_nothrow_move_assignable.hpp(29): note: see reference to class template instantiation 'boost::hash<K>' being compiled 1> with 1> [ 1> K=std::string 1> ] 1>d:\...\boost\unordered\detail\implementation.hpp(2739): note: see reference to class template instantiation 'boost::is_nothrow_move_assignable<H>' being compiled 1> with 1> [ 1> H=boost::hash<std::string> 1> ] 1>d:\...\boost\unordered\detail\implementation.hpp(2902): note: see reference to class template instantiation 'boost::unordered::detail::functions<boost::hash<K>,std::equal_to<K>>' being compiled 1> with 1> [ 1> K=std::string 1> ] 1>d:\...\boost\unordered\unordered_map.hpp(60): note: see reference to class template instantiation 'boost::unordered::detail::table<boost::unordered::detail::map<A,K,T,H,P>>' being compiled 1> with 1> [ 1> A=std::allocator<std::pair<const std::string,example_namespace::my_custom_class_t>>, 1> K=std::string, 1> T=example_namespace::my_custom_class_t, 1> H=boost::hash<std::string>, 1> P=std::equal_to<std::string> 1> ] 1>d:\...\my_model.cpp(47): note: see reference to class template instantiation 'boost::unordered::unordered_map<std::string,example_namespace::my_custom_class_t,boost::hash<K>,std::equal_to<K>,std::allocator<std::pair<const K,T>>>' being compiled 1> with 1> [ 1> K=std::string, 1> T=example_namespace::my_custom_class_t 1> ] s中？

在boost :: unordered_map中存储boost :: recursive_variant_类型失败

0 个答案: