常量引用如何产生影响？(How does constant reference makes a difference?)

 我不明白为什么以下代码不起作用： 
 
#include <iostream>
using namespace std;

class PayOff{};
class PayOffCall : public PayOff{};

class PayOffBridge{
public:
    PayOffBridge( PayOff& innerPayOff){};
};

class VanilaOption{
public:
   VanilaOption(PayOffBridge& ThePayOff_){cout << " test " <<endl;}
};


int main () {
PayOffCall thePayOff;
VanilaOption theOption(thePayOff);
  return 0;
}
 
 出于某种原因，在VanilaOption类（下面的代码）中更改对const的引用使其工作，有人可以解释它是如何工作的吗？ 我得到的错误是： 没有匹配函数来调用'VanilaOption :: VanilaOption（PayOffCall＆）' 
 
 但它并没有帮助我弄明白。 
 
class VanilaOption{
public:
   VanilaOption(const PayOffBridge& ThePayOff_){cout << " test " <<endl;}
};
 
 我也不明白为什么在PayOffBridge引用预期有效时通过PayOffCall引用，有人可以帮我解决这个问题吗？ 
 
 谢谢！ 

I dont understand why the following code doesn't work:
 
#include <iostream>
using namespace std;

class PayOff{};
class PayOffCall : public PayOff{};

class PayOffBridge{
public:
    PayOffBridge( PayOff& innerPayOff){};
};

class VanilaOption{
public:
   VanilaOption(PayOffBridge& ThePayOff_){cout << " test " <<endl;}
};


int main () {
PayOffCall thePayOff;
VanilaOption theOption(thePayOff);
  return 0;
}
 
For some reason changing the reference to const in VanilaOption class (code below) makes it work, can someone explain how does it work? The error I get is: no matching function for call to 'VanilaOption::VanilaOption(PayOffCall&)'
 
but it doesn't help me to figure it out. 
 
class VanilaOption{
public:
   VanilaOption(const PayOffBridge& ThePayOff_){cout << " test " <<endl;}
};
 
I also don't understand why passing PayOffCall reference when PayOffBridge reference is expected works, can someone help me out on this?
 
Thank you!

原文：https://stackoverflow.com/questions/34583750