Question

以下代码使用VC 15.3.5编译得很好：

#include <Windows.h>
#include <string>
#include <memory>
#include <optional>
#include <functional>

class TypeDictionary;
class IStructureField {};

using  FieldFactory = std::function<std::unique_ptr<IStructureField>(TypeDictionary& dict, LPCSTR szName, std::optional<ULONG> ulOffset, std::optional<std::string> strFieldType, std::optional<ULONG> ulFieldSize)>;


int main()
{
FieldFactory ff;

ff = [](TypeDictionary& dict, LPCSTR szName, std::optional<ULONG> ulOffset, std::optional<std::string> szFieldType, std::optional<ULONG> ulFieldSize) -> std::unique_ptr<IStructureField> {
    return  std::unique_ptr<IStructureField>();
};

    return 0;
}

它使用15.4.0生成以下错误消息：

1>f:\projects\fullpath\fullpath\fullpath.cpp(22): error C2679: binary '=': no operator found which takes a right-hand operand of type 'main::<lambda_36489dce1cc59e5a8de4329a29806b5a>' (or there is no acceptable conversion)
1>c:\program files (x86)\microsoft visual studio\2017\enterprise\vc\tools\msvc\14.11.25503\include\functional(656): note: could be 'std::function<std::unique_ptr<IStructureField,std::default_delete<_Ty>> (TypeDictionary &,LPCSTR,std::optional<ULONG>,std::optional<std::string>,std::optional<ULONG>)> &std::function<std::unique_ptr<_Ty,std::default_delete<_Ty>> (TypeDictionary &,LPCSTR,std::optional<ULONG>,std::optional<std::string>,std::optional<ULONG>)>::operator =(std::nullptr_t) noexcept'
1>        with
1>        [
1>            _Ty=IStructureField
1>        ]
1>c:\program files (x86)\microsoft visual studio\2017\enterprise\vc\tools\msvc\14.11.25503\include\functional(629): note: or       'std::function<std::unique_ptr<IStructureField,std::default_delete<_Ty>> (TypeDictionary &,LPCSTR,std::optional<ULONG>,std::optional<std::string>,std::optional<ULONG>)> &std::function<std::unique_ptr<_Ty,std::default_delete<_Ty>> (TypeDictionary &,LPCSTR,std::optional<ULONG>,std::optional<std::string>,std::optional<ULONG>)>::operator =(std::function<std::unique_ptr<_Ty,std::default_delete<_Ty>> (TypeDictionary &,LPCSTR,std::optional<ULONG>,std::optional<std::string>,std::optional<ULONG>)> &&)'
1>        with
1>        [
1>            _Ty=IStructureField
1>        ]
1>c:\program files (x86)\microsoft visual studio\2017\enterprise\vc\tools\msvc\14.11.25503\include\functional(612): note: or       'std::function<std::unique_ptr<IStructureField,std::default_delete<_Ty>> (TypeDictionary &,LPCSTR,std::optional<ULONG>,std::optional<std::string>,std::optional<ULONG>)> &std::function<std::unique_ptr<_Ty,std::default_delete<_Ty>> (TypeDictionary &,LPCSTR,std::optional<ULONG>,std::optional<std::string>,std::optional<ULONG>)>::operator =(const std::function<std::unique_ptr<_Ty,std::default_delete<_Ty>> (TypeDictionary &,LPCSTR,std::optional<ULONG>,std::optional<std::string>,std::optional<ULONG>)> &)'
1>        with
1>        [
1>            _Ty=IStructureField
1>        ]
1>f:\projects\fullpath\fullpath\fullpath.cpp(22): note: while trying to match the argument list '(FieldFactory, main::<lambda_36489dce1cc59e5a8de4329a29806b5a>)'
1>Done building project "FullPath.vcxproj" -- FAILED.

正如我在cppcon上看到的那样（斯蒂芬的演讲），<functional>已经完成了很多工作......这有关系吗？我犯了什么错误？

解决方法也没问题。

Edit1：添加了两个包含文件，以帮助理解问题不存在：同样的错误...

Edit2：修复我的VS安装后，代码刚编译完毕。但是，原始代码没有。之前我曾遇到https://developercommunity.visualstudio.com/content/problem/74313/compiler-error-in-xsmf-control-with-stdoptional-pa.html并试图解决这个问题（这暴露了我面临的问题）。没有解决方法，代码编译（但再次点击__this问题......）。

使用VC 15.4.0，std :: function赋值生成C2679（用15.3.5编译）

0 个答案: