创建 std::promise<std::tuple<T>> 时出现错误 C2512（仅限 Visual Studio）

Posted 2023-02-22

【中文标题】创建 std::promise<std::tuple<T>> 时出现错误 C2512（仅限 Visual Studio）

【英文标题】：Error C2512 when creating a std::promise<std::tuple<T>> (Visual Studio-only)

【发布时间】：2021-09-22 19:09:06

【问题描述】：

在创建类型 (T) 没有默认构造函数的 std::promise<std::tuple<T>> 时遇到错误（仅限 Visual Studio）。

我创建了一个派生示例来突出这个问题。

#include <future>
#include <tuple>

class Foo 
public:
    Foo() = delete;

    Foo(int value) :
        mValue value  

    

private:
    int mValue;
;

int main()

    std::promise<std::tuple<Foo>> p;

1>------ Build started: Project: ConsoleApplication1, Configuration: Debug Win32 ------
1>ConsoleApplication1.cpp
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.27.29110\include\future(206): error C2512: 'std::tuple<Foo>::tuple': no appropriate default constructor available
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.27.29110\include\future(203): message : while compiling class template member function 'std::_Associated_state<_Ty>::_Associated_state(std::_Deleter_base<_Ty> *)'
1>        with
1>        [
1>            _Ty=std::tuple<Foo>
1>        ]
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.27.29110\include\future(1143): message : see reference to function template instantiation 'std::_Associated_state<_Ty>::_Associated_state(std::_Deleter_base<_Ty> *)' being compiled
1>        with
1>        [
1>            _Ty=std::tuple<Foo>
1>        ]
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.27.29110\include\future(1143): message : see reference to class template instantiation 'std::_Associated_state<_Ty>' being compiled
1>        with
1>        [
1>            _Ty=std::tuple<Foo>
1>        ]
1>C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.27.29110\include\future(1143): message : while compiling class template member function 'std::promise<std::tuple<Foo>>::promise(void)'
1>C:\Users\Quenton Jones\source\repos\ConsoleApplication1\ConsoleApplication1\ConsoleApplication1.cpp(22): message : see reference to function template instantiation 'std::promise<std::tuple<Foo>>::promise(void)' being compiled
1>C:\Users\Quenton Jones\source\repos\ConsoleApplication1\ConsoleApplication1\ConsoleApplication1.cpp(22): message : see reference to class template instantiation 'std::promise<std::tuple<Foo>>' being compiled
1>Done building project "ConsoleApplication1.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

使用clang编译时没有问题。

为什么 Visual Studio 要求 T 具有默认构造函数？

【问题讨论】：

known issue - We’ve investigated this issue and found that fixing it will break our ABI. To preserve binary compatibility, we don’t allow ABI breakages within the current release of the library.

【参考方案1】：

为了解决这个已知问题，我执行了以下操作：

class Foo 
public:
#if _WIN32
    Foo() 
        throw std::exception("Invalid Constructor");
    
#else
    Foo() = delete;
#endif

    Foo(int value) :
        mValue value  

    

private:
    int mValue;
;

【参考方案2】：

错误 C2512 的常见原因是当您定义一个带参数的类或结构构造函数时，然后您尝试声明一个不带任何参数的类或结构的实例。有关详细信息，请参阅此document。

还有一点，目前std::promise不能用非默认可构造类型编译。使用#if，#else也是一种方式。