#pragma pack(push, 1)
struct A
{
    char a;
    int b;
    double c;
    char d[11];
};
#pragma pack(pop)

#pragma pack(push, 2)
struct B
{
    char a;
    int b;
    double c;
    char d[11];
};
#pragma pack(pop)

void main()
{
    cout << sizeof(A) << endl;
    cout << sizeof(B) << endl;
}

char buffer[] = "......";
void *ptr = buffer;
std::size_t space = sizeof(buffer) - 1;
std::align(alignof(int),sizeof(char),pt,space);

// 实现boost中的optional类
// 该类可以存储任意类型的数据
// int float string struct

#pragma once
using namespace std;

template <typename T>
class COptional
{
public:
    // alignof是vs2013ctp中才支持的版本，如果没有该版本，用alignedment_of<T>::value代替
    //typedef aligned_storage<sizeof(T), alignof(T)>::type AligendT;
    using AligendT = typename aligned_storage<sizeof(T), alignment_of<T>::value>::type;

    COptional(){}
    COptional(const T &t)
    {
        Create(t);
    }
    COptional(const COptional& other)
    {
        if (other.IsInit())
        {
            Assign(other);
        }
    }
    ~COptional()
    {
        if (IsInit())
        {
            Destroy();
        }
    }

    const T & operator*() const
    {
        if (IsInit())
        {
            return *((T *)(&m_Data));
        }
        cout << "is not init!" << endl;
    }

    // 根据参数创建
    template<typename ...ARGS>
    void Emplace(ARGS&& ...Args)
    {
        Destroy();
        Create(forward<ARGS>(Args)...);
    }

private:
    template <typename ...ARGS>
    void Create(ARGS&& ...Args)
    {
        new (&m_Data) T(forward<ARGS>(Args)...);  // placement new 创建
        m_bInit = true;
    }

    // 销毁缓冲区对象
    void Destroy()
    {
        if (m_bInit)
        {
            m_bInit = false;
            ((T *)(&m_Data))->~T();
        }
    }

    bool IsInit() const
    {
        return m_bInit;
    }

    void Assign(const COptional& other)
    {
        if (other.IsInit())
        {
            Destroy();
            new (&m_Data) (T)*((T*)(&other.m_Data));
            m_bInit = true;
        }
        Destroy();
    }
private:
    AligendT m_Data;
    bool m_bInit = false;
};

#pragma once

#include<type_traits>
#include<boost\optional.hpp>

using namespace std;

// 实现懒惰求值类lazy
template<typename T>
class CLazy
{
public:
    CLazy(){}

    template<typename FUN, typename ...ARG>
    CLazy(FUN &fun, ARG ...args)
    {
        std::cout << "参数个数：" << sizeof ...(args) << std::endl;
        m_fun = [&fun, args...]{return fun(args...); };
    }

    T &Value()
    {
        if (!m_Value.is_initialized())
        {
            m_Value = m_fun();   // 隐士转换
        }

        return *m_Value;
    }

    bool IsCreated() const
    {
        return m_Value.is_initialized();
    }

private:
    std::function<T()> m_fun;
    boost::optional<T> m_Value;
};

#include "stdio.h"

#include "lazy.h"

#include<iostream>
using namespace std;

#include "optionalex.h"

int foo(int x)
{
    cout << "函数名:" << __FUNCTION__ << endl;
    return 2 * x;
}

float fooadd(int x, int y, float z)
{
    cout << "函数名:" << __FUNCTION__ << endl;
    return x + y+z;
}

template<typename FUN, typename ...ARG>
CLazy<typename result_of<FUN(ARG...)>::type> lazy(FUN && fun, ARG && ...args)
{
    return CLazy<typename result_of<FUN(ARG...)>::type>(forward<FUN>(fun), forward<ARG>(args)...);
}

struct test
{
    int a;
    float b;
    test(int aa, float bb) :a(aa), b(bb){}
    friend ostream& operator<<(ostream& os, const test& other)
    {
        os << other.a << " " << other.b << endl;
        return os;
    }
};
void main()
{
    cout << "COptional类测试1,当对象没初始化：" << endl;
    COptional<int> op1;
    cout << "输出：" << *op1 << endl;

    cout << "COptional类测试2,int类型：" << endl;
    COptional<int> op2 = 99;
    cout << "输出：" << *op2 << endl;

    cout << "COptional类测试3,float类型：" << endl;
    COptional<float> op3 = 12.453;
    cout << "输出：" << *op3 << endl;
    
    cout << "COptional类测试4,struct类型：" << endl;
    COptional<test> op4 = test(8, 9.8);
    cout << "输出：" << *op4 << endl;

    cout << "lazy类测试:" << endl;
    CLazy<int> lazy1(foo, 2);
    cout << lazy1.Value() << endl;
    CLazy<float> lazy22(fooadd, 2, 4, 6.2);
    cout << lazy22.Value() << endl;
    cout << lazy([](int a, int b){return a + b; }, 10, 22).Value() << endl;
}