写一个 Move aware class

文章目录

class MyString {
public:
    static size_t DCtor;
    static size_t Ctor;
    static size_t CCtor;
    static size_t CAsgn;
    static size_t MCtor;
    static size_t Dtor;
private:
    char* _data;
    size_t _len;
    void _init_data(const char *s) {
        _data = new char[_len + 1];
        memcpy(_data, s, _len);
        _data[_len] = '\0';
    }
public:
    // default ctor
    MyString(): _data(NULL), _len(0) {
        ++DCtor;
    }
    // ctor
    MyString(const char* p): _len(strlen(p)) {
        ++Ctor;
        _init_data(p);
    }
    
    // copy ctor
    MyString(const Mystring& str):_len(str._len) {
        ++CCtor;
        _init_data(str._data);
    }
    
    // move ctor
    MyString(MyString&& str) noexcept
        :_data(str._data), _len(str._len) {
        ++MCtor;
        str._len = 0;
        str._data = NULL;// IMPORTANT
    }
    
    // copy assignment
    MyString& operator=(const MyString& str) {
        ++CAsgn;
        if(this != &str) {  // 自我赋值检查
            if(_data) delete _data;
            _len = str._len;
            _init_data(str._data);
        } else {
            
        }
        return *this;
    }
    
    // move assignment
    MyString& operator=(MyString&& str) noexcept{
        ++MAsgn;
        if(this != &str) {  // 自我赋值检查
            if(_data) delete _data;
            _len = str._len;
            _data = str._data;
            str._len = 0;
            str._data = NULL;
        }
        return *this;
    }
    
    // dtor
    virtual ~MyString() {  
        ++Dtor;
        if(_data) delete _data;
    }
    
    // operator<
    bool operator<(const MyString& rhs) const {
        return string(this->data) < string(rhs._data);
    }
    // operator==
    bool operator==(const MyString& rhs) const {
        return string(this->data) == string(rhs._data); 
    }
   
    char* get() const { return _data; } 
}


size_t MyString::DCtor = 0;
size_t MyString::Ctor = 0;
size_t MyString::CCtor = 0;
size_t MyString::CAsgn = 0;
size_t MyString::MCtor = 0;
size_t MyString::Dtor = 0;
size_t MyString::MAsgn = 0;
namespace std {
template<>
struct hash<MyString> { // for unordered containers
    size_t operator() (const MyString& s) const noexcept {
        return hash<string>()(string(s.get()));
        // 借用现成的 hash<string>
    }
}
}