如何初始化一系列不可移动，不可复制的对象？ [英] How to initialize a sequence of non-movable, non-copyable objects?

问题描述

假设我有一个既不可移动也不可复制的类型：

Let's say I have a type which is neither movable nor copyable:

struct foo
{
  explicit foo( size_t ){}
  ~foo(){}

  foo( foo const & ) = delete;
  foo( foo && ) = delete;
  foo& operator=( foo const & ) = delete;
  foo& operator=( foo & ) = delete;
};

现在给定编译时已知的数字（称为N）在堆栈上创建一个序列，每个序列用数字0到N-1初始化？我会满意一个C风格的数组 foo [N] ， std :: array< foo，N> ，或者甚至可以是某种 std :: tuple 。

Now given a number known at compile time (call it N), is there any way that I can create a "sequence" of these on the stack with each one initialized with numbers 0 through N-1? I would be satisfied with a C-style array foo[N], a std::array< foo, N >, or perhaps even a std::tuple of some kind.

我想避免的是写出：

foo f0( 0 ), f1( 1 ), ... fNminus1( N-1 );

当感觉这是编译器应该能为我做的事情。我已经能够想出的最好的是使用 boost :: optional 。

when it feels like this is something the compiler should be able to do for me. The best I've been able to come up with is using boost::optional.

boost::optional< foo > f[N];

for( size_t i = 0U; i < N; ++i )
  f[i] = boost::in_place( i );

但这依赖于运行时逻辑，即使所有必需的信息在编译时可用。另外，我还剩下一些类似指针数组的东西。

But that relies on runtime logic even though all the required information is available at compile-time. Plus, I'm left with something that behaves like an array of pointers.

推荐答案

// create a type with the proper alignment
typedef std::aligned_storage<sizeof(foo), std::alignment_of<foo>::value>::type buffer_type;

const int N = 10;
// create an array of uninitialized raw data
buffer_type storage_buffer[N];

// initialize each foo object with placement new
for (size_t i=0; i<N; ++i)
    new (storage_buffer + i) foo(i);

foo * fp = (foo*)(&storage_buffer);
// access your foo objects via fp


// you must manually call the destructor of each object
for (size_t i=0; i<N; ++i)
    fp[i].~foo();

如果这看起来很麻烦，那就是。但你可以很容易地把这个功能封装在一个类中。

If that seems like a lot of hassle, it is. But you could easily encapsulate that functionality in a class.

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