CS246 Lecture Notes - Lecture 20: Idiom

• School: University of Waterloo
• Department: Computer Science
• Course: CS246
• Professor: Nomair Naeem

Document Summary

We want subclasses to be able to place/provide some behaviour while other remain the same. Thus, all turtle classes must have heads and feet drawn similiarly. It"s a good idea to make the methods drawhead() drawfeet() drawshell() private because you can"t draw parts of turtle. You can only call draw() to draw the entire turtle. 9 class turtle public: void draw() // this is not virtual. // template to draw a turtle drawhead(); drawshell(); drawfeet(); 22 virtual void drawshell() = 0; // the only difference between turtles is the color you draw the shell. 7 class redturtle : public turtle voic drawshell() override. This example uses the nvi idom- non-virtual interface. Consider a public virtual methods. public: part of the interface, comes with pre/post conditions. virtual: invitation to subclasses to modify behaviour. Final question what must you do to use nvi idiom? public methods must be non-virtual all virtual methods are private (except for the destructor)