std :: bind，this和QtConcurrent [英] std::bind, this and QtConcurrent

问题描述

我试图使用 std :: bind 将绑定到<$ c $中使用的方法c> QtConcurrent :: blockingMapped

标题：

  class TuringMachine 
 {
 private：
 TRTable table; 
 std :: set< ConfigNode *> currentConfigs; 
 
 //函数对象
 std :: function< std :: set< ConfigNode *>（const TuringMachine *，ConfigNode *）> step_f; 
 //方法它将保存
 std :: set< ConfigNode *> step（TuringMachine * this_m，ConfigNode * parent）; 
 
 std :: set< ConfigNode *>& makeStep（）; 
  

}

>

  TuringMachine :: TuringMachine（/ ** /）
 {
 
 step_f = std :: bind （& TuringMachine :: step，this，std :: placeholders :: _ 1）; 
} 
 
 std :: set< ConfigNode *> & TuringMachine :: makeStep（）{
 
 auto configSet = QtConcurrent :: blockingMapped< QLinkedList< std :: set< ConfigNode *>>（currentConfigs，step_f）; //并发执行！ 
 
 / ** / 
 return currentConfigs; 
} 
 std :: set< ConfigNode *> TuringMachine :: step（TuringMachine * this_m，ConfigNode * parent）{//实际步骤
 / ** / 
} 
  

所以，我在这里做每个配置节点 >在 currentConfigs 中。 Im使用 std :: bind 将绑定到到步骤所以它只需要一个参数，如在 blockingMapped 的文档中。

获取

 错误： std :: _Bind< std :: _ Mem_fn< std :: set< ConfigNode *>（TuringMachine :: *）（TuringMachine *，ConfigNode *）>（TuringMachine *，std :: _ Placeholder< 1& const TuringMachine *，ConfigNode *）'
 ... / Qt / 474 / gcc / include / QtCore / qtconcurrentmapkernel.h：121：错误：没有匹配的调用'（std :: function< std :: set< ; ConfigNode *>（const TuringMachine *，ConfigNode *）>）（ConfigNode * const&）'
 ... / Qt / 474 / gcc / include / QtCore / qtconcurrentmapkernel.h：136：error：no匹配以调用'（std :: function< std :: set< ConfigNode *>（const TuringMachine *，ConfigNode *）>）（ConfigNode * const&）'
  / pre> 
 
 
和注意：预期有2个参数，提供1个参数 
 
 $ b b 
我错了什么？
 
 
 
  EDIT  
 
 
 
工作版本（供未来参考）：
 
 
 
标题：
  // function object 
 std :: function< std :: set< ConfigNode *>（ConfigNode *）> step_f; 
 //方法它将保存
 std :: set< ConfigNode *> step（ConfigNode * parent）; 
  
资料来源：
 code> TuringMachine :: TuringMachine（/ ** /）
 {
 step_f = std :: bind（& TuringMachine :: step，this，std :: placeholders :: _ 1）; 
} 
  
 
 
解决方案
如果要绑定成员函数，你必须通过一个这个指针，在你的情况下，这将意味着你必须通过2  this  -pointers：
 
 
 
正常调用成员函数：
  struct bar {
 int a; 
 void foo（）{
 std :: cout<< a<< std :: endl; 
} 
 
 void call_yourself（）{
 auto f = std :: bind（& bar :: foo，this）; 
 f（）; 
} 
}; 
  
您的情况：
  step_f = std :: bind（& TuringMachine :: step，this，this，std :: placeholders :: _ 1）; 
  
没有理解你的代码，我可能会重新编写你的代码， $ c> this 指针。
 
Im trying to use std::bind to bind this to method that is used in QtConcurrent::blockingMapped

Header:
class TuringMachine
{
private:
    TRTable table;
    std::set<ConfigNode*> currentConfigs;

    //function object
    std::function<std::set<ConfigNode*>( const TuringMachine*, ConfigNode*)> step_f;
    //method it will hold
    std::set<ConfigNode *> step(TuringMachine* this_m ,ConfigNode *parent);

    std::set<ConfigNode*>& makeStep();
}

Source:
    TuringMachine::TuringMachine(/**/)  
{

    step_f = std::bind(&TuringMachine::step, this, std::placeholders::_1);
}

std::set<ConfigNode*> &TuringMachine::makeStep(){

    auto configSet = QtConcurrent::blockingMapped<QLinkedList<std::set<ConfigNode*>>>(currentConfigs, step_f);//concurrent execution!

   /**/ 
   return currentConfigs;
}
std::set<ConfigNode*> TuringMachine::step(TuringMachine *this_m, ConfigNode * parent){     //the actual step
  /**/
}
So what Im doing here is running step conncurrently with blockingMapped on each ConfigNode in currentConfigs. Im using std::bind to bind this to step so it only requires one argument, as in the documentation of blockingMapped. 

Im getting
error: no match for call to '(std::_Bind<std::_Mem_fn<std::set<ConfigNode*> (TuringMachine::*)(TuringMachine*, ConfigNode*)>(TuringMachine*, std::_Placeholder<1>)>) (const TuringMachine*, ConfigNode*)'
.../Qt/474/gcc/include/QtCore/qtconcurrentmapkernel.h:121: error: no match for call to '(std::function<std::set<ConfigNode*>(const TuringMachine*, ConfigNode*)>) (ConfigNode* const&)'
.../Qt/474/gcc/include/QtCore/qtconcurrentmapkernel.h:136: error: no match for call to '(std::function<std::set<ConfigNode*>(const TuringMachine*, ConfigNode*)>) (ConfigNode* const&)'
And note: 2 arguments expected, 1 provided

Where did I go wrong?

EDIT

Corrected, working version (for future "reference"):

Header:
    //function object
    std::function<std::set<ConfigNode*>( ConfigNode*)> step_f;
    //method it will hold
    std::set<ConfigNode *> step(ConfigNode *parent);
Source:
    TuringMachine::TuringMachine(/**/)  
{
    step_f = std::bind(&TuringMachine::step, this, std::placeholders::_1);
}

解决方案
If you want to bind a member function, you would have to pass a this pointer, which in your case would mean that you would have to pass 2 this-pointers:

Normal call to member function:
struct bar {
  int a;
  void foo() {
    std::cout << a << std::endl;
  }

  void call_yourself() {
     auto f = std::bind(&bar::foo, this);
     f();
  }
};
Your case:
    step_f = std::bind(&TuringMachine::step, this, this,std::placeholders::_1);
Without understanding your code, I would probably redesing your code such that you can avoid the double this pointer.

                        
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