contained object with no default constructor and no initialization on declaration
contained const data member
contained reference data member
base class with no default constructor
Constructor Inheritance
Constructor Delegation
Copy Constructor
The default one performs member-wise copy, which is not shallow copy nor deep copy!
對於 pointer 來說是 shallow copy 但是對於 string or vector 來說是 deep copy
Constructor implicit casting
the explicit keyword
when to use the explicit keyword?
when the full state of the object being created is passed in to the constructor, for example, the string object. In contrast, the vector object is not, so the explicit keyword is used in its constructor
Rule of Zero
When your class does not need any resource management
Use properly managed data members: std::string, std containers, std::unique_ptr, std::shared_ptr
Rule of Three
When you need a destructor
Block the copy and assignment constructor first! And then check it you need to implement them
Rule of Five
If you implement or block any of the five, you lose the defaults for the move operations
make sure to ask back for the defaults if they are fine(use the default keyword)
Inheritance
State Pattern
Encapsulate varying behavior based on object’s state
