OutlineVirtue DemoLinear Data Structure DemoTemplatesOutline Virtue Linear TemplatesCPSC 427a: Object-Oriented ProgrammingMichael J. FischerLecture 15October 28, 2010CPSC 427a 1/22Outline Virtue Linear TemplatesVirtue DemoLinear Data Structure DemoTemplatesCPSC 427a 2/22Outline Virtue Linear TemplatesVirtue DemoCPSC 427a 3/22Outline Virtue Linear TemplatesVirtual virtueclass Basic {public:virtual void print(){cout <<"I am basic. "; }};class Virtue : public Basic {public:virtual void print(){cout <<"I have virtue. "; }};class Question : public Virtue {public:void print(){cout <<"I am questing. "; }};CPSC 427a 4/22Outline Virtue Linear TemplatesMain virtueWhat does this do?int main (void) {cout << "Searching for Virtue\n";Basic* array[3];array[0] = new Basic();array[1] = new Virtue();array[2] = new Question();array[0]->print();array[1]->print();array[2]->print();return 0;}See demo 15a-Virtue!CPSC 427a 5/22Outline Virtue Linear TemplatesLinear Data Structure DemoCPSC 427a 6/22Outline Virtue Linear TemplatesUsing polymorphismSimilar data structures:ILinked list implementation of a stack of items.ILinked list implementation of a queue of items.Both support a common interface:Ivoid push(Item*)IItem* pop()IItem* peek()Iostream& print(ostream&)They differ only in where push() places a new item.The demo 15b-Virtual (from Chapter 15 of textbook) showshow to exploit this commonality.CPSC 427a 7/22Outline Virtue Linear TemplatesInterface fileWe define this common interface by the abstract class.class Container {public:virtual void put(Item*) =0;virtual Item* pop() =0;virtual Item* peek() =0;virtual ostream& print(ostream&) =0;};Any class derived from it is required to implement these fourfunctions.We could derive Stack and Queue directly from Container, butwe instead exploit even more commonality between these twoclasses.CPSC 427a 8/22Outline Virtue Linear TemplatesClass Linearclass Linear: public Container {protected: Cell* head;private: Cell* here; Cell* prior;protected: Linear();virtual ~Linear ();void reset();bool end() const;void operator ++();virtual void insert( Cell* cp );virtual void focus() = 0;Cell* remove();void setPrior(Cell* cp);public: void put(Item * ep);Item* pop();Item* peek();virtual ostream& print( ostream& out );};CPSC 427a 9/22Outline Virtue Linear TemplatesExample: Stackclass Stack : public Linear {public:Stack(){}~Stack(){}void insert( Cell* cp ) { reset(); Linear::insert(cp); }void focus(){ reset(); }ostream& print( ostream& out ){out << " The stack contains:\n";return Linear::print( out );}};CPSC 427a 10/22Outline Virtue Linear TemplatesExample: Queueclass Queue : public Linear {private:Cell* tail;public:Queue() { tail = head; }~Queue(){}void insert( Cell* cp ) {setPrior(tail); Linear::insert(cp); tail=cp; }void focus(){ reset(); }};CPSC 427a 11/22Outline Virtue Linear TemplatesClass structureClass structure.IContainer specifies the common interface.ILinear contains the bulk of the code. It is derived fromContainer.IStack and Queue are both derived from Linear.ICell is a “helper” class that is aggregated by Linear.IItem is the base type for the container elements. It is definedby a typedef here but would normally be specified by atemplate.IExam is a non-trivial item type used by main to illustratestacks and queues.CPSC 427a 12/22Outline Virtue Linear TemplatesC++ featuresThe demo illustrates several C++ features.1. [Container] Pure abstract class.2. [Cell] Friend functions.3. [Cell] Printing a pointer in hex.4. [Cell] Operator extension operator Item*().5. [Linear] Virtual functions and polymorphism.6. [Linear] Scanner pairs (prior, here) for traversing a linked list.7. [Linear] Operator extension operator ++()8. [Linear, Exam] Use of private, protected, and publicin same class.CPSC 427a 13/22Outline Virtue Linear Templates#include structureGetting #include’s in theright order.Problem: Making surecompiler sees symboldefinitions before they areused.Partial solution: Make de-pendency graph. If notcyclic, each .hpp file in-cludes the .hpp files justabove it.exam.hppitem.hppcontainer.hpplinear.hppqueue.hppstack.hppcell.hppCPSC 427a 14/22Outline Virtue Linear TemplatesTemplatesCPSC 427a 15/22Outline Virtue Linear TemplatesTemplate overviewTemplates are instructions for generating code.Are type-safe replacement for C macros.Can be applied to functions or classes.Allow for type variability.Example:template <class T>class FlexArray { ... };Later, can instantiateclass RandString : FlexArray<const char*> { ... };and useFlexArray<const char*>::put(store.put(s, len));CPSC 427a 16/22Outline Virtue Linear TemplatesTemplate functionsDefinition:template <class X> void swapargs(X& a, X& b) {X temp;temp = a;a = b;b = temp;}Use:int i,j;double x,y;char a, b;swapargs(i,j);swapargs(x,y);swapargs(a,b);CPSC 427a 17/22Outline Virtue Linear TemplatesSpecializationDefinition:template <> void swapargs(int& a, int& b) {// different code}This overrides the template body for int arguments.CPSC 427a 18/22Outline Virtue Linear TemplatesTemplate classesLike functions, classes can be made into templates.template <class T>class FlexArray { ... };makes FlexArray into a template class.When instantiated, it can be used just like any other class.For a flex array of ints, the name is FlexArray<int>.No implicit instantiation, unlike functions.CPSC 427a 19/22Outline Virtue Linear TemplatesCompilation issuesRemote (non-inline) template functions must be compiled andlinked for each instantiation.Two possible solutions:1. Put all template function definitions in the .hpp file alongwith the class definition.2. Put template function definitions in a .cpp file as usual butexplicitly instantiate.E.g., template class FlexArray(int); forces compilationof the int instantiation of FlexArray.CPSC 427a 20/22Outline Virtue Linear TemplatesTemplate parametersTemplates can have multiple parameters.Example:template<class T, int size> declares a template with twoparameters, a type parameter T and an int parameter size.Template parameters can also have default values.Used when parameter is omitted.Example:template<class T=int, int size=100> class A { ... }.A<double> instantiates A to type A<double, 100>.A<50> instantiates A to type A<int, 50>.CPSC 427a 21/22Outline Virtue Linear TemplatesUsing template classesDemo 15c-Evaluate implements a simple expression evaluatorbased on a precedence parser.It derives a template class Stack<T> from the template classFlexArray<T> introduced in 13-Hangman-full.The precedence parser