emplace_back初始化列表错误，当初始化列表在独立变量上工作时

所以我一直在做一个对象池类，它是这样用的：

class MagicTrick {
public:
MagicTrick(int magic) : _magic(magic)
{}
int predict() {
return _number * _magic;
}
private:
int _magic;
int _number = 2;
};
const std::size_t poolSize = 1;
ObjectPool<MagicTrick> magicTrickPool(poolSize, 5);
const int number = magicTrickPool.schedule([](MagicTrick& magicTrick){
return magicTrick.predict();
});

这工作正常，但是当线程池使用的对象删除其复制构造函数时，例如数据成员是池构造失败std::unique_ptr。 在内部，我使用一个向量来存储池：

struct ObjectAndLock {
Object object;
bool free;
static bool isFree(const ObjectAndLock& objectAndLock) {
return objectAndLock.free;
}
};
std::vector<ObjectAndLock> objectAndLocks;

我构造了完整的池类：

template<typename Object> 
class ObjectPool {
template<typename ...Args>
ObjectPool(std::size_t poolSize, Args&&... objectArgs) 
: objectAndLocks(poolSize, { {std::forward<Args>(objectArgs)...}, true}) 
{}

这将使用此处列出的第三个重载构造向量 https://en.cppreference.com/w/cpp/container/vector/vector

但是，这会将元素复制到向量中。 所以我把它改成emplace_back，在向量中构造对象，如下所示：

template<typename Object> 
class ObjectPool {
template<typename ...Args>
ObjectPool(std::size_t poolSize, Args&&... objectArgs)
{
if(poolSize == 0){
throw std::runtime_error("poolSize must be greater than 0");
}
objectAndLocks.reserve(poolSize);
for (std::size_t i = 0; i < poolSize; i++)
{
objectAndLocks.emplace_back({Object{std::forward<Args>(objectArgs)...}, true});
}
}
} 

但是，这会导致以下错误：

ProjectsObjectPoolpublic_includeObjectPoolObjectPool.hpp(87): error C2660: 'std::vector<object_pool::ObjectPool<MagicTrick>::ObjectAndLock,std::allocator<_Ty>>::emplace_back': function does not take 1 arguments
with
[
_Ty=object_pool::ObjectPool<MagicTrick>::ObjectAndLock
]
C:Program Files (x86)Microsoft Visual Studio2019CommunityVCToolsMSVC14.23.28105includevector(651): note: see declaration of 'std::vector<object_pool::ObjectPool<MagicTrick>::ObjectAndLock,std::allocator<_Ty>>::emplace_back'
with
[
_Ty=object_pool::ObjectPool<MagicTrick>::ObjectAndLock
]

但是，我可以使用初始值设定项列表在构造函数中创建一个对象，如下所示，它可以很好地编译。

ObjectAndLock hello = { Object{std::forward<Args>(objectArgs)...}, true };

我已经看到了这个答案，但是我无法让它工作： emplace_back不适用于 std：：vector<std：：map><int，>> 我使用std::initializer_list的诱惑作为：

std::initializer_list<ObjectAndLock>

也许这是错误的？

所以我的问题是我如何让emplace_back正常工作？我最多可以使用 c++17

下面是一个失败的示例类，因为它不可复制：

struct NonCopyable {
std::unique_ptr<int> number = std::make_unique<int>(10);
NonCopyable(const NonCopyable& other) = delete;
NonCopyable& operator=(const NonCopyable& other) = delete;
};

为了完整起见，这里是完整的类：

#ifndef OBJECTPOOL_H
#define OBJECTPOOL_H
#include <vector>
#include <functional>
#include <map>
#include <mutex>
#include <condition_variable>
#include <type_traits>
#include <algorithm>
#include <stdexcept>
#include <exception>
namespace object_pool {
namespace internal {
template <typename Function>
class DeferToDestruction {
Function _function;
public:
DeferToDestruction(Function function) : _function(function) {}
~DeferToDestruction() { _function(); }
};
}
template<typename Object> 
class ObjectPool {
public:
/*!
@brief Create an object pool for 
@param poolSize - Size of object pool, this must be atleast 1
@param objectArgs... - Arguments to construct the objects in the pool
Complete Example:
@code
class MagicTrick {
public:
MagicTrick(int magic) : _magic(magic)
{}
int predict() {
return _number * _magic;
}
private:
int _magic;
int _number = 2;
};
std::size_t poolSize = 5;
object_pool::ObjectPool<MagicTrick> magicTrickPool(poolSize, 5);
const int number = magicTrickPool.schedule([](MagicTrick& magicTrick){
return magicTrick.predict();
});
@endcode
Zero Argument Constructor Example:
@code            
struct ZeroArgs {
int number = 2;
};
object_pool::ObjectPool<ZeroArgs> zeroArgsPool(1);
@endcode
Multiple Argument Constructor Example:
@code
class MultiArgs {
public:
MultiArgs(std::string name, int age, bool alive) {
_number = name.size() + age + (alive ? 5 : -5);
}
int predict() {
return _number * 2;
}
private:
int _number = 2;
};
object_pool::ObjectPool<MultiArgs> multiArgsPool(1, "bob", 99, true);
@endcode
*/
template<typename ...Args>
ObjectPool(std::size_t poolSize, Args&&... objectArgs)
{
if(poolSize == 0){
throw std::runtime_error("poolSize must be greater than 0");
}
objectAndLocks.reserve(poolSize);
for (std::size_t i = 0; i < poolSize; i++)
{
objectAndLocks.emplace_back({Object{std::forward<Args>(objectArgs)...}, true});
}
}
~ObjectPool(){ 
std::unique_lock<std::mutex> lock(objectAndLocksMutex);            
const auto allobjectAndLocksFree = [this]() {
return std::all_of(std::begin(objectAndLocks), std::end(objectAndLocks), ObjectAndLock::isFree);
};
if(allobjectAndLocksFree()) {
return;
}
conditionVariable.wait(lock, allobjectAndLocksFree);
}
/*!
@brief Schedule access to the pool
@param callback - An callable with the the argument being a reference to the class stored in the object pool.
@return Returns return from the callback function, including void
Simple Example:
@code
const int number = magicTrickPool.schedule([](MagicTrick& magicTrick){
return magicTrick.predict();
});
@endcode
*/
template<typename FunctionWithObjectAsParameter>
auto schedule(FunctionWithObjectAsParameter&& callback)
{
const auto findFreeObject = [this]() {
return std::find_if(std::begin(objectAndLocks), std::end(objectAndLocks), ObjectAndLock::isFree);
};
std::unique_lock<std::mutex> lock(objectAndLocksMutex);
auto freeObject = findFreeObject();
if(freeObject == std::end(objectAndLocks)) {
conditionVariable.wait(lock, [this, &freeObject, &findFreeObject]{
freeObject = findFreeObject();
return freeObject != std::end(objectAndLocks);
});
}
freeObject->free = false;
lock.unlock();
internal::DeferToDestruction freeAndUnlockAndNotify([this, &freeObject] () {
{
std::scoped_lock<std::mutex> lock(objectAndLocksMutex);
freeObject->free = true;
}
conditionVariable.notify_one();
});
return callback(freeObject->object);
}
private:    
struct ObjectAndLock {
Object object;
bool free;
static bool isFree(const ObjectAndLock& objectAndLock) {
return objectAndLock.free;
}        
};
std::vector<ObjectAndLock> objectAndLocks;
std::mutex objectAndLocksMutex;
std::condition_variable conditionVariable;
};
}
#endif