MWE很长，还请大家多多包涵。 简而言之，我想使用一个抽象对象工厂来创建从基类派生的对象，派生对象成为单例并使用 shared_ptr 传递。 到目前为止，如果单例不是从单例模板派生的，则一切正常。
假设一个具有以下结构:
class Base{}
class Derived1 : public Base {} // public Base, public Singleton<Derived1>
class Derived2 : public Base {}
我想使用我的抽象对象工厂来生成派生类，但要确保它只创建一次，否则将 std::shared_ptr 返回给派生对象。
我已经实现了一个单例模板和一个对象工厂，如果我想创建不是从任何东西派生的对象，它可以很好地工作:
单例:
template<class Derived>
class Singleton{
private:
static std::shared_ptr<Derived> instance_;
public:
template <typename... Args>
static
std::shared_ptr<Derived> Instance(Args... args){
if (instance_ == nullptr){
instance_ = std::shared_ptr<Derived>(
new Derived(std::forward<Args>(args)...) );
}
return instance_;
}
};
template <class T> std::shared_ptr<T> Singleton<T>::instance_ = nullptr;
对象工厂:
template <class Object, typename... Args>
class Abstract_Factory_Base {
protected:
using Factories_Map = std::unordered_map<std::string, std::shared_ptr<Abstract_Factory_Base<Object, Args... >> >;
static Factories_Map* factories_; ///< \brief stores factories able to construct objects derived from "Object" template parameter
public:
Factories_Map* factories(){
if(factories_ == nullptr){
factories_ = new Factories_Map;
}
return factories_;
}
static
std::shared_ptr<Abstract_Factory_Base<Object, Args...>>
Type(const std::string &key){
return (*factories_)[key];
};
virtual
std::shared_ptr<Object>
create(const Args &... args) = 0;
};
template <class Object, class Derived, typename... Args>
class Abstract_Factory : public Abstract_Factory_Base<Object, Args...>{
public:
std::shared_ptr<Object>
create(const Args &... args){
return std::shared_ptr<Derived>(
new Derived(args...));
}
};
template <class Object, class Derived, typename... Args>
class Factory_Register : public Abstract_Factory<Object, Derived, Args...>{
public:
Factory_Register(const std::string& key){
//static_assert(!(std::is_base_of<Singleton<Derived>, Derived>::value), "");
this->factories()->emplace(
key,
std::shared_ptr<Abstract_Factory_Base<Object, Args...>>(
new Abstract_Factory<Object, Derived, Args...>));
}
};
template <class Object, class Derived, typename... Args>
class Singleton_Factory : public Abstract_Factory_Base<Object, Args...>{
public:
std::shared_ptr<Object> create(const Args &... args){
return Derived::Instance(args...);
}
};
template <class Object, class Derived, typename... Args>
class Singleton_Factory_Register : public Singleton_Factory<Object, Derived, Args...>{
public:
Singleton_Factory_Register(const std::string& key){
//static_assert(std::is_base_of<Singleton<Derived>, Derived>::value, "");
this->factories()->emplace(
key,
std::shared_ptr<Abstract_Factory_Base<Object, Args...>>(
new Singleton_Factory<Object, Derived, Args...>));
}
};
假设我现在想将它用于:
class Foo{
protected:
int x_, y_;
public:
Foo(){x_ = 0; y_ = 0;}
Foo(int x, int y){
x_=x;
y_=y;
}
void print(){
std::cout << x_+y_ << std::endl;
}
};
using Foo_Factory = Abstract_Factory_Base<Foo,int,int>;
class FooFoo : public Singleton<FooFoo>, public Foo{
friend class Singleton<FooFoo>;
using FooFoo_Register = Singleton_Factory_Register<
Foo,
FooFoo,
int,
int>;
static FooFoo_Register reg;
protected:
//int x_,y_;
FooFoo(){};
FooFoo(int x, int y){
x_=2*x;
y_=2*y;
}
public:
void print(){
std::cout << x_ << std::endl;
}
};
template <class Object, typename... Args>
typename Abstract_Factory_Base<Object, Args...>::Factories_Map* Abstract_Factory_Base<Object, Args...>::factories_;
FooFoo::FooFoo_Register FooFoo::reg("foofoo");
int main(){
std::shared_ptr<FooFoo> foofoo1, foofoo2, foofoo3;
foofoo1 = Foo_Factory::Type("foofoo")->create(1,2); // this fails
Foo_Factory::Type("foofoo"); // this calls ok
////foofoo2 = Foo_Factory::Type("foofoo")->create(10,10);
////foofoo3 = Foo_Factory::Type("foofoo")->create(2,10);
////printf("(%p, %p, %p)\n", foofoo1.get(), foofoo2.get(), foofoo3.get());
//printf("(%p)\n", foofoo1.get());
//foofoo1->print();
////foofoo2->print();
////foofoo3->print();
}
我遇到了很多编译错误，关于移动的提示，自过去几个小时以来我一直无法解决。
你能帮帮我吗，或者把我重定向到某个地方。我想要至少有可能吗？谢谢!
In file included from /usr/include/c++/5/bits/shared_ptr.h:52:0,
from /usr/include/c++/5/memory:82,
from main.cpp:2:
/usr/include/c++/5/bits/shared_ptr_base.h: In instantiation of ‘std::__shared_ptr<_Tp, _Lp>& std::__shared_ptr<_Tp, _Lp>::operator=(std::__shared_ptr<_Tp1, _Lp>&&) [with _Tp1 = Abstract_Factory_Base<Foo, int, int>; _Tp = FooFoo; __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2u]’:
/usr/include/c++/5/bits/shared_ptr.h:302:4: required from ‘std::shared_ptr<_Tp>& std::shared_ptr<_Tp>::operator=(std::shared_ptr<_Tp1>&&) [with _Tp1 = Abstract_Factory_Base<Foo, int, int>; _Tp = FooFoo]’
main.cpp:180:13: required from here
/usr/include/c++/5/bits/shared_ptr_base.h:1008:4: error: no matching function for call to ‘std::__shared_ptr<FooFoo, (__gnu_cxx::_Lock_policy)2u>::__shared_ptr(std::remove_reference<std::__shared_ptr<Abstract_Factory_Base<Foo, int, int>, (__gnu_cxx::_Lock_policy)2u>&>::type)’
__shared_ptr(std::move(__r)).swap(*this);
^
/usr/include/c++/5/bits/shared_ptr_base.h:1146:7: note: candidate: std::__shared_ptr<_Tp, _Lp>::__shared_ptr(const std::__weak_ptr<_Tp, _Lp>&, std::nothrow_t) [with _Tp = FooFoo; __gnu_cxx::_Lock_policy _Lp = (__gnu_cxx::_Lock_policy)2u]
__shared_ptr(const __weak_ptr<_Tp, _Lp>& __r, std::nothrow_t)
^
/usr/include/c++/5/bits/shared_ptr_base.h:1146:7: note: candidate expects 2 arguments, 1 provided
/usr/include/c++/5/bits/shared_ptr_base.h:1094:2: note: candidate: template<class _Alloc, class ... _Args> std::__shared_ptr<_Tp, _Lp>::__shared_ptr(std::_Sp_make_shared_tag, const _Alloc&, _Args&& ...)
__shared_ptr(_Sp_make_shared_tag __tag, const _Alloc& __a,
^
/usr/include/c++/5/bits/shared_ptr_base.h:1094:2: note: template argument deduction/substitution failed:
/usr/include/c++/5/bits/shared_ptr_base.h:1008:4: note: cannot convert ‘std::move<std::__shared_ptr<Abstract_Factory_Base<Foo, int, int>, (__gnu_cxx::_Lock_policy)2u>&>((* & __r))’ (type ‘std::remove_reference<std::__shared_ptr<Abstract_Factory_Base<Foo, int, int>, (__gnu_cxx::_Lock_policy)2u>&>::type {aka std::__shared_ptr<Abstract_Factory_Base<Foo, int, int>, (__gnu_cxx::_Lock_policy)2u>}’) to type ‘std::_Sp_make_shared_tag’
__shared_ptr(std::move(__r)).swap(*this);
最佳答案
我认为问题在于 foofoo1 = Foo_Factory::Type("foofoo")您尝试分配类型为 std::shared_ptr<Abstract_Factory_Base<Foo,int,int>> 的对象到一个 std::shared_ptr<FooFoo> .这些类型之间没有转换。
要解决这个问题，您需要使用返回的工厂对象来创建您要存储的对象:
foofoo1 = Foo_Factory::Type("foofoo")->create(...);
为 FooFoo 使用适当的参数构造函数被传递给 create .
关于具有抽象工厂的派生类的 C++11 单例，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/44117029/