什么是C ++中的类型擦除? [英] What is type erasure in C++?
问题描述
因此,我正在阅读有关类型擦除的文章。但是该文章中的代码似乎部分不正确,例如:
So I was reading this article about type erasure. But the code in that article seems partially incorrect, for example:
template <typename T>
class AnimalWrapper : public MyAnimal
{
const T &m_animal;
public:
AnimalWrapper(const T &animal)
: m_animal(animal)
{ }
const char *see() const { return m_animal.see(); }
const char *say() const { return m_animal.say(); }
};
其后是
void pullTheString()
{
MyAnimal *animals[] =
{
new AnimalWrapper(Cow()), /* oO , isn't template argument missing? */
....
};
}
这些错误使我无法继续阅读本文。
These mistakes discouraged me from reading any further in the article.
无论如何;任何人都可以通过简单的示例来说明C ++中的类型擦除是什么意思吗?
Anyways; can anyone please teach what type erasure in C++ means, with simple examples?
我想了解一下它,以了解 std :: function
可行,但无法解决。
I wanted to learn about it to understand how std::function
works, but couldn't get my head around it.
推荐答案
下面是一个非常简单的类型示例删除操作:
Here's a very simple example of type erasure in action:
// Type erasure side of things
class TypeErasedHolder
{
struct TypeKeeperBase
{
virtual ~TypeKeeperBase() {}
};
template <class ErasedType>
struct TypeKeeper : TypeKeeperBase
{
ErasedType storedObject;
TypeKeeper(ErasedType&& object) : storedObject(std::move(object)) {}
};
std::unique_ptr<TypeKeeperBase> held;
public:
template <class ErasedType>
TypeErasedHolder(ErasedType objectToStore) : held(new TypeKeeper<ErasedType>(std::move(objectToStore)))
{}
};
// Client code side of things
struct A
{
~A() { std::cout << "Destroyed an A\n"; }
};
struct B
{
~B() { std::cout << "Destroyed a B\n"; }
};
int main()
{
TypeErasedHolder holders[] = { A(), A(), B(), A() };
}
如您所见, TypeErasedHolder
可以存储对象,并正确销毁它们。重要的一点是,它不对所支持的类型施加任何限制(1):例如,它们不必从公共基础派生。
As you can see, TypeErasedHolder
can store objects of an arbitrary type, and destruct them correctly. The important point is that it does not impose any restrictions on the types supported(1): they don't have to derive from a common base, for example.
(1)当然除了可移动。
这篇关于什么是C ++中的类型擦除?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!