c ++我可以使用std :: unique_ptr与依赖注入吗？ [英] c++ Can I use std::unique_ptr with dependency injection?

问题描述

我一直在使用原始指针进行依赖注入，我决定将我的代码转换为使用shared_ptr。这工作，但我想知道如果我可以使用unique_ptr而不是？在下面的例子中，MyClass将管理信用卡服务的生命周期。

  class PaymentProcessor 
 {
 PaymentProcessor（?? creditCardService）：
：creditCardService_ ）
 {
 
} 
 
 private：
 CreditCardService * creditCardService_; 
} 
 
 class MyClass 
 {
 public：
 void DoIt（）
 {
 creditCardService_.reset（new VisaCardService ））; 
 PaymentProcessor pp（creditCardService_）; 
 pp.ProcessPayment（）; 
} 
 
 private：
 std :: unique_ptr< CreditCardService> creditCardService_; 
} 
  

你可以传递一个unique_ptr到另一个类， 指针（没有拥有它？）？如果是这样，这是一个好主意，参数的类型应该在PaymentProcessor的构造函数中？

UPDATE

在上面的例子中，我可以在堆栈上创建一个 VisaCardService 变量，并且 PaymentProcessor 构造函数将此作为参考参数。这似乎是推荐的C ++实践。然而，在具体类型的creditCardService_在运行时间之前是未知的（例如，用户选择特定的信用卡服务在运行时使用），使用 std :: unique_ptr $ block


您可以将unique_ptr传递给另一个类，其中其他类是
只是使用指针（不拥有它？）

指向参考的指针：

  class PaymentProcessor 
 {
 public：
 PaymentProcessor（CreditCardService& creditCardService_）：
：creditCardService_（creditCardService_）
 {
} 
 
 private：
 CreditCardService& creditCardService_; 
}; 
 
 void DoIt（）
 {
 creditCardService_.reset（new VisaCardService（））; 
 PaymentProcessor pp（* creditCardService_）; 
 pp.ProcessPayment（）; 
} 
  

如果您仍然想使用指针，则需要使用 get 方法：

  class PaymentProcessor 
 {
 public ：
 PaymentProcessor（CreditCardService * creditCardService_）：
：creditCardService_（creditCardService_）
 {
} 
 private：
 CreditCardService * creditCardService_; 
}; 
 
 void DoIt（）
 {
 creditCardService_.reset（new VisaCardService（））; 
 PaymentProcessor pp（creditCardService_.get（））; 
 pp.ProcessPayment（）; 
} 
  

I had been doing dependency injection using raw pointers and I decided to convert my code to use shared_ptr. This works but I'm wondering if I could use unique_ptr instead? In my example below, MyClass would manage the lifetime of the credit card service.

class PaymentProcessor
{
    PaymentProcessor(?? creditCardService):
      :creditCardService_(creditCardService)
      {

      }

private:
   CreditCardService *creditCardService_;     
}

class MyClass
{ 
public:
   void DoIt()
   {
     creditCardService_.reset(new VisaCardService());
     PaymentProcessor pp(creditCardService_);
     pp.ProcessPayment();
   }

private:   
   std::unique_ptr<CreditCardService> creditCardService_;
}

Can you pass a unique_ptr to another class where the other class is just "using" the pointer (without owning it??)? If so is this a good idea and what should the type of the parameter be in the constructor for PaymentProcessor?

UPDATE

In the example as shown above I can alternatively create a VisaCardService variable on the stack and have the PaymentProcessor constructor take this as a reference parameter. This seems to be the recommended C++ practice. However, in the case where the concrete type of creditCardService_ is not known until runtime (e.g., the user chooses the particular Credit Card Service to use at runtime), is using std::unique_ptr with references the best solution?

解决方案

Can you pass a unique_ptr to another class where the other class is just "using" the pointer (without owning it??)?

In that case, change the pointer to reference :

class PaymentProcessor
{
public:
    PaymentProcessor(CreditCardService & creditCardService_):
      :creditCardService_(creditCardService_)
      {
      }

private:
   CreditCardService &creditCardService_;     
};

   void DoIt()
   {
     creditCardService_.reset(new VisaCardService());
     PaymentProcessor pp(*creditCardService_);
     pp.ProcessPayment();
   }

If you still want to use a pointer, then you need to use get method :

class PaymentProcessor
{
public:
    PaymentProcessor(CreditCardService * creditCardService_):
      :creditCardService_(creditCardService_)
      {
      }
private:
   CreditCardService *creditCardService_;     
};

   void DoIt()
   {
     creditCardService_.reset(new VisaCardService());
     PaymentProcessor pp(creditCardService_.get());
     pp.ProcessPayment();
   }

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