Question

#include <iostream>
#include <memory>
#include <cstdlib>

class IBase
{
public:
    IBase() = default;
    virtual ~IBase() = default;
    virtual void f1() = 0;
};

class IDerived
{
public:
    IDerived() = default;
    virtual ~IDerived() = default;
    virtual void f2() = 0;
};

class BaseImpl : public IBase
{
public:
    BaseImpl() = default;
    virtual ~BaseImpl() override = default;
    virtual void f1() override { /* serious code */}
};

class DerivedImpl : public BaseImpl, public IDerived
{
public:
    DerivedImpl() = default;
    virtual ~DerivedImpl() override = default;
    virtual void f2() override { /* serious code */}
};

class Base : public IBase
{
public:
    Base() : m_impl(std::make_shared<BaseImpl>()) {}
    virtual ~Base() override = default;
    virtual void f1() override { m_impl->f1(); }

protected:
    Base(const std::shared_ptr<BaseImpl>& impl) : m_impl(impl) {}
    std::shared_ptr<BaseImpl> m_impl;
};

class Derived : public Base, public IDerived
{
public:
    Derived() : Base(std::make_shared<DerivedImpl>()) {}
    virtual ~Derived() override = default;
    virtual void f2() override { impl()->f2(); }

private:
    std::shared_ptr<DerivedImpl> impl() { return std::dynamic_pointer_cast<DerivedImpl>(m_impl); }
};

int main()
{
    Base base;
    base.f1();

    Derived derived;
    derived.f1();
    derived.f2();

    std::cin.sync();
    std::cin.get();
    return EXIT_SUCCESS;
}

它有效，但看起来很奇怪我可能会放弃pimpl。

Answer 1

想象一下你的Base定义如下：

class Base {
public:
    Base();
    virtual ~Base();
    virtual void f1();

protected:
    class Impl;
    Impl *p_impl; // or shared_ptr, or unique_ptr, or whatever you like.
};

请注意，Base::Impl没有定义任何内容。这是PIMPL习惯用语中非常重要的一部分，因为您可能必须使用Impl类中的元素，这些元素需要#include - 您不希望包含在标题类中的内容。

派生类看起来像这样：

class Derived: public Base {
public:
    Derived();
    ~Derived();
    virtual void f1(); // or not, depends
    virtual void f2();

protected:
    class Impl2;
    Impl2 *p_impl2; // note that Derived::Impl2 might inherit from Base::Impl
};

这仍然隐藏了Base和Derived中Base::Impl和Derived::Impl2的实施细节，同时让您完全自由地以任何方式实施Derived你喜欢（包括继承）。

Answer 2

您的Impl类应该只包含私有变量和方法。

不要在那里放置任何需要儿童课程的东西。对Impl类进行子类化是错误的C ++方法，因为这会破坏这种模式的目的。

这是实现支持继承的pimpl的有效方法吗？

2 个答案: