C++ Pimpl

一般写法：

Test.h

class Test
{
public:
    Test(int a, int b);
    ~Test();

    Test(const Test& other);
    Test(Test&& other);

    Test& operator=(const Test& other);
    Test& operator=(Test&& other);

    int GetResult();

private:
    struct Impl;
    std::unique_ptr<Impl> _impl;
};

Test.cpp

struct Test::Impl
{
    // Test's private fields and member functions here

    int calcResult()
	{
        return a * b + a + b;
    }

    int a{ 0 };
    int b{ 0 };
};

Test::Test(int a, int b)
    : _impl(new Impl())
{
    _impl->a = a;
    _impl->b = b;
}

Test::~Test()
{
    // Note: because std::unique_ptr will be destruct automatically
    //_impl = nullptr;
}

Test::Test(const Test& other)
    : _impl(new Impl(*other._impl))
{
}

Test::Test(Test&& other)
    : _impl(std::move(other._impl))
{
}

Test& Test::operator=(const Test& other)
{
    // we still need this to avoid memory allocation
    if (this == &other) {
        return *this;
    }

    _impl = std::unique_ptr<Impl>(new Impl(*other._impl));
    
    return *this;
}

Test& Test::operator=(Test&& other)
{
    // Note: because std::unique_ptr has checked for this condition
    //if (this == &other) {
    //	return *this;
    //}

    _impl = std::move(other._impl);

    return *this;
}

int Test::GetResult()
{
    return _impl->calcResult();
}

没有其它指针数据，构造和赋值可简化为：

Test::Test(Test&&) = default;
Test::Test(const Test&) = delete; // 需要写在头文件里
Test& Test::operator=(Test&&) = default;
Test& Test::operator=(const Test&) = delete; // 需要写在头文件里

也就是：

Test

// Test.hpp
class Test
{
public:
    Test();
    ~Test();
    
    Test(Test&& other);
    Test(const Test& other) = delete;
    
    Test& operator=(Test&& other);
    Test& operator=(const Test& other) = delete;
    
private:
    struct Impl;
    std::unique_ptr<Impl> _impl;
}

// Test.cpp
struct Test::Impl
{
}

Test::Test()
    : _impl(std::make_unique<Impl>())
{
}

Test::~Test() = default;

Test::Test(Test&& other) = default;
Test& Test::operator=(Test&& other) = default;