使用仿函数或lambda进行矢量深度复制 [英] vector deep copy using a functor or lambda

问题描述

我正在尝试复制std :: shared_ptr向量的深层副本。不幸的是，我不能使用对象，因为大多数指针都指向多态对象。

I am trying to make deep copies of vectors of std::shared_ptr. Unfortunately I can't use objects, as most of those pointers are to polymorphic objects.

我尝试使用适合于std :: shared_ptr：的克隆方法：

I've tried using the clone method adapted to std::shared_ptr:

std::shared_ptr<Action> Clone ( )
{
  return std::make_shared<Action>( *this );
}

但是我仍然遇到问题。
因此，我想知道（不记得在哪里看过）如何通过使用执行实际深度复制的函数或lambda将一个向量的内容复制到另一个向量中。

But I am still running into problems. So, I was wondering (can't remember where I've seen it) how can I copy the contents of one vector into another, by using a function or a lambda that performs the actual deep copy.

让我改写一下，我不仅想要指针，我也想要指向的对象的副本。
典型任务

Let me rephrase, I don't want just the pointers, I want a copy of the pointed objects too. The typical assignment

operator=

std :: vector的

似乎只复制指针，正如人们通常期望的那样。

for std::vector appears to copy only the pointers as one would normally expect.

我正在使用GCC 4.8如果可能的话，可以使用C ++ 11。

I'm using GCC 4.8 with C++11 in case it can offer any more elegant or minimalistic approach.

实际目的是使具有这些向量的类的副本构造函数提供非共享对象，但指针相同或不同：

The actual purpose is so that copy constructors of classes that have those vectors, provide non-shared objects but same or different pointers:

class State
{
public:
  State ( const State & rhs )
  {
    // Deep copy Actions here?
  }


private:
  std::vector<std::shared_ptr<Action>> _actions;
};

非常感谢能提供帮助的人！

Many thanks to anyone who can help!

推荐答案

要深度复制/克隆类型擦除的类型，克隆函数需要是虚拟的

To deep-copy/clone a type-erased type the cloning function needs to be virtual

struct Action {
    virtual std::shared_ptr<Action> clone() const =0;
};
struct Paste : public Action {  
    virtual std::shared_ptr<Action> clone() const 
    {return std::make_shared<Paste>(*this);}
};

一旦有了，就可以使用 transform 和一个简单的lambda。

Once you have that, then you can use transform and a simple lambda.

std::vector<std::shared_ptr<Action>> ActionList = {...};

auto cloner = [](const std::shared_ptr<Action>& ptr) 
    -> std::shared_ptr<Action> 
    {return ptr->clone();};

std::vector<std::shared_ptr<Action>> Copy;
std::transform(ActionList.begin(), ActionList.end(), std::back_inserter(Copy), cloner);

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