使用forward_as_tuple在旧式函数签名上传递参数包 [英] passing a parameter pack over a legacy function signature using forward_as_tuple

问题描述

在我的应用程序中，我想在旧式函数签名上传递参数包，并更改值.这是通过尝试作为注释来说明我的问题的代码:

In my app I would like to pass in a parameter pack over a legacy function signature, and change the values. Here is code that illustrates my question with my attempts as comments:

#include <tuple>
#include <cassert>

void LegacySignature( void* param );

template< typename... ArgsT >
// using ???; // attempt: can 'template alias' or 'using declaration' make the pack's type visible so I can use it inside the LegacyFunction?
void MyFunc( ArgsT&... args )
{
  auto userArgsTuple = std::forward_as_tuple< ArgsT&... >( args... );

  LegacySignature( &userArgsTuple );
}

void LegacySignature( void* param )
{
//  auto userArgsTuple = reinterpret_cast<???>( param ); // attempt: how can I get the parameter pack's type declared so I can use it here?

  // do something with the params like change num to 44 and tf to true;
  //userArgsTuple->num = 44; // desired functionality
  //userArgsTuple->tf = true; // desired functionality
}

int main()
{
  int num { 33 };
  bool tf { false };
  MyFunc( num, tf );
  assert( num == 44 && tf == true );

  return 0;
}

有没有办法使参数包成为可声明的左值?

Is there a way to make the parameter pack a declarable lvalue?

推荐答案

下面的代码修复了示例代码，以便回答有关如何使用forward_as_tuple在旧式函数签名上传递参数包的问题.

The code below fixes the sample code so that it answers the question as to how to pass a parameter pack over a legacy function signature using forward_as_tuple.

#include <tuple>
#include <cassert>
#include <memory>
#include <functional>

#define ARGSET int, bool

void LegacySignature( long* param ); // ie, LPARAM

template< typename... ArgsT >
struct MyParams
{
  MyParams( ArgsT... args ) : rvalRefs { std::forward_as_tuple( args... ) } {} // The resulting forward_as_tuple tuple has rvalue reference data members 
  std::tuple< ArgsT... > rvalRefs;
};


void LegacySignature( long* legSigParam )
{
  auto userArgsTuple( reinterpret_cast< MyParams< ARGSET >* >( legSigParam ) );

  // do something with the params like change num to 44 and tf to true;
  std::get< 0 >( userArgsTuple->rvalRefs ) = 44; // index types can probably be worked out using enums
  std::get< 1 >( userArgsTuple->rvalRefs ) = true;
}

int main()
{
  int num { 33 };
  bool tf { false };
  MyParams< ARGSET > myParams( num, tf );

  std::unique_ptr< MyParams< ARGSET > > legSigParamPtr = std::make_unique< MyParams< ARGSET > >( myParams );
  LegacySignature( ( long* )legSigParamPtr.get() );
  assert( std::get< 0 >( legSigParamPtr->rvalRefs ) == 44 && std::get< 1 >( legSigParamPtr->rvalRefs ) == true );

  return 0;
}

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