一 偏特化实现hash function
型如：
template<>
struct hash <string>
二 tuple 使用
tuple<XX,XX,XX> t; XX: 为类型
tuple <XX,XX,XX> t (YY,YY,YY); XX：为类型 YY：为具体值
make_tuple(XX,YY,ZZ);
获取get<XX>(t) XX为序号
课程中讲到的GNU C4.8 版本， tuple具体实现使用了递归的思路
最新版本gcc7.2 中的tuple由
tuple 继承 _Tuple_impl ,, _Tuple_impl Basis case of inheritance recursion.
三 type traits
http://en.cppreference.com/w/cpp/header/type_traits
通过模板泛化，特化实现
四 cout
重载operator<<
五 movable
通过修改指针方式完成， 效率比较copy高，但是具有破化性。
六 作业报错
重载operator<< , 输出参数使用版本参数， 报错如下
meter me
cout << me << endl;
^test.h:142:52: error: ‘std::ostream& weida1001::operator<<(std::ostream&)’ must take exactly two arguments std::ostream & operator << (ostream& os const T &m) { ^test.cpp: In function ‘void weida1001::test()’:test.cpp:21:8: error: no match for ‘operator<<’ (operand types are ‘std::ostream {aka std::basic_ostream}’ and ‘weida1001::meter’)
//@{ /** * @brief Character inserters * @param __out An output stream. * @param __c A character. * @return out * * Behaves like one of the formatted arithmetic inserters described in * std::basic_ostream. After constructing a sentry object with good * status, this function inserts a single character and any required * padding (as determined by [22.2.2.2.2]). @c __out.width(0) is then * called. * * If @p __c is of type @c char and the character type of the stream is not * @c char, the character is widened before insertion. */ templateinline basic_ostream<_CharT, _Traits>&
参考 C++ include ostream 文件， 进行修改， 输出char 和string 不同， 我这里只是用char
template < typename _CharT, typename _Traits, typename T>
basic_ostream<_CharT,_Traits>&
operator<<(basic_ostream<_CharT, _Traits>&os, const T &m)
{
unit_traits<T>u;
os << m.getvalue() << u.get_unit(m);
}
