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motivation

why should we use operators at all?

operators allow you to convey meaning about types that functions don't

  • what must be true of a type T for us to be able to use min?

    • T should have an ordering relationship that makes sense.
    • T should represent something comparable,ordered concept,where a minimum can be logically determined

  • how do operators work with classes>?

  • like declare a fun in a class,declare an ooperator's functionality
  • 使用时就像常规的函数或者操作
  • 与函数重载一样。if we give the same name,it will override the operator's behavior

不可以重载的操作符

  • scop resolution : ::
  • ternary : ?
  • member access: .
  • pointer to member access: .*
  • object size ,type,and casting:sizeof(),typeid(),cast()

两种重载方式

  1. member overloading

  2. declares the overloaded operator within the scope of your class

  3. non-member overloading

  4. declare outside
  5. define both the left and right hand objects as parameters

non-member overloading

preferred by stl,more idiomatic c++ reasons * allows for the left hand side to be a non class type * allows us to overload operators with classes we donot own

bool operator < (const stanfordid& lhs,const stanfordid &rhs); 对比 bool stanfordid::operator < (const stanfordid &rhs) cosnt {};

Note

左右操作数都作为参数传进了函数里

关于成员变量

成员操作符重载可以访问this->and 类中的变量

freindkeywoed 可以让非成员函数/类访问另一个类的private information * 如何使用？ 在头文件中声明重载函数为freind

rules and philosophies

  • because operators are intended to convey meaning about a type,the meaning should be obvious
  • the operators that we can define are oftentimes arithmetic optors.the functionality should be reasonably similar to their corresponding operations
  • if the meaning is not obvious,define a func known as the Principle of Least Astonishment(PoLA)

in general

  • good practices like the rule of contrariety
  • define == != return !(*this==other)

<<

  • a lot of flexibility