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由于各种内部原因，我正在使用的库要求与其模板一起使用的类是可移动的和可分配的。我写了一个类，并给它一个显式的移动构造函数。

#pragma once
#include <entt.hpp>

namespace ECS {
    //! Abstract base class for all components.
    class Component {
        friend class Transform;
    private:
        entt::registry* p_registry; //!< The registry to which this component belongs.
        entt::entity m_entity = entt::null; //!< The entity to which this component belongs.
        bool m_knownEntity = false;

        virtual void checkEntity() {
            m_knownEntity = true;
            m_entity = entt::to_entity(*p_registry, *this);
        }
    public:
        Component(entt::registry& registry) :
            p_registry(&registry) {}

        Component(Component&& old) noexcept :
            p_registry(nullptr) {
            *this = std::move(old);
        }
        virtual Component& operator=(Component&& old) {
            if (this != &old) {
                p_registry = old.p_registry;
                m_entity = old.m_entity;
                m_knownEntity = false;
            }
            return *this;
        }

        inline entt::entity getEntity() { if (m_knownEntity) { checkEntity(); } return m_entity; }
        entt::registry& getRegistry() { return *p_registry; }

        virtual void initialise() = 0; //!< Called once per component. During object creation, is called after all the object's components have been created.
        virtual void terminate() = 0; //!< Called once per component. During object destruction, is called before any of the object's components have been deleted.
    };
}

但是，这些静态断言中的第一个失败了：

static_assert(std::is_move_constructible_v<ECS::Component>, "ECS::Component isn't move constructible."); // Fails
static_assert(std::is_move_assignable_v<ECS::Component>, "ECS::Component isn't move assignable."); // Passes

我错过了什么？这真是令人费解，我在网上找不到任何关于为什么具有显式声明的移动构造函数的类可能无法移动构造的任何信息。是因为它是一个抽象类吗？任何帮助将不胜感激。

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1 回答 1

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is_move_constructible是基于 的行为is_constructibe；只是is_constructible<T, T&&>。并is_constructible<T, ...>要求您可以这样做：

T t(...);

当然，对于抽象类，这是你做不到的。因此，就目前而言，没有抽象类可以“移动构造” is_move_constructible。

于 2020-07-25T23:35:00.373 回答