对象大小固定的单线程内存池设计

类Rational通过重载new和delete以实现高效的内存分配，提高程序性能。
具体设计方案如下：

class Rational{public:    Rational(int a = 0, int b = 1)        :n(a), d(b)    {}    void* operator new(size_t size){        return memPool->alloc(size);    }    void operator delete(void* doomed, size_t size){        memPool->free(doomed);    }private:    int n;    int d;    static MemoryPool<Rational>* memPool;};/*    以下为内存分配与回收类## 标题 ##的实现*/template <class T>class MemoryPool{public:    MemoryPool(size_t size = EXPANSION_SIZE);    ~MemoryPool();    inline void* alloc(size_t size);    inline void free(void* someElement);private:    //空闲列表的下一个元素    MemoryPool<T>* next;    //如果空闲列表为空，就按该大小扩展它    enum{ EXPANSION_SIZE = 32};    //添加空闲元素至空闲列表    void expandTheFreeList(inthowMany = EXPANSION_SIZE);};template <class T>MemoryPool<T>::MemoryPool(size_t size){    expandTheFreeList(size);}//析构函数  遍历空间列表，并删除所有元素template <class T>MemoryPool<T>::~MemoryPool(){    MemoryPool* nextPtr = next;    for (nextPtr = next; nextPtr != NULL; nextPtr = next){        next = next->next;        delete[] nextPtr;    }}//分配内存template <class T>inlinevoid* MemoryPool<T>::alloc(size_t){    if (!next){//内存用尽则调用expandTheFreeList扩充        expandTheFreeList();    }    MemoryPool<T>* head = next;    next = head->next;    return head;}//将内存回收到空闲列表template <class T>inlinevoid MemoryPool<T>::free(void* doomed){    MemoryPool<T>* head = static_cast<MemoryPool<T>*>(doomed);    head->next = next;    next = head;}//expandTheFreeList向堆中分配新元素，然后将它们连接到空闲列表中//当空闲列表被用尽时调用template <class T>void MemoryPool<T>::expandTheFreeList(int howMany){    //分配足够大的对象已包含下一个指针    size_t size = (sizeof(T) > sizeof(MemoryPool<T>*)) ?        sizeof(T) : sizeof(MemoryPool<T>*);    MemoryPool<T>* runner = static_cast<MemoryPool<T>*>(new char[size]);    next = runner;    for (int i = 0; i < howMany; i++){        runner->next = static_cast<MemoryPool<T>*>new char[size];        runner = runner->next;    }    runner->next = 0;}

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读书笔记：《提高C++性能的编程技术》