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Linguagens Dinâmicas são Melhores para Implemen...

Linguagens Dinâmicas são Melhores para Implementar OO

Palestra apresentada na RubyConf Brasil 2012

cassiomarques

August 30, 2012
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  1. package br.com.rubyconf; public class FlyingCat implements FlyingAnimal,Feline { public void

    talk() { // implementation... } public void fly() { // implementation... } }
  2. class A { public: void foo() { cout << "calling

    A's implementation" << endl; }; };
  3. class B : public A { public: void foo() {

    cout << "calling B's implementation" << endl; } }; class C : public A { public: void foo() { cout << "calling C's implementation" << endl; } };
  4. class D : public B, public C { }; int

    main (int argc, char const* argv[]) { D d = D(); d.foo(); return 0; }
  5. teste.cpp|50 error| error: request for member ‘foo’ is ambiguous teste.cpp|26

    error| error: candidates are: void A::foo() teste.cpp|39 error| error: void C::foo() teste.cpp|33 error| error: void B::foo()
  6. class Product include Sellable include Discountable def price super -

    super * discount end end item = Product.new puts item.price # 13.5
  7. class Product end product = Product.new puts product.price # undefined

    method `price' for #<Product: 0x00000105ab7e70> (NoMethodError)
  8. ou

  9. class BaseClass # ... end class OurClass < BaseClass #

    ... end some_object = OurClass.new some_object.do_something
  10. some_object.do_something Singleton class OurClass included modules included modules BaseClass Object

    (nativo) Module Kernel (nativo) BasicObject (nativo) undefined method `do_something' for #<OurClass: 0x0000010450fe88> (NoMethodError)
  11. C++

  12. class Vehicle { public: void virtual move() = 0; void

    setColor(string _color) { color = _color; } private: string color; };
  13. class Car : public Vehicle { public: void move() {

    cout << "Moving..." << endl; } };
  14. package br.com.rubyconf; public abstract class Vehicle { private String color;

    public abstract void move(); public void setColor(String color) { this.color = color; } }
  15. package br.com.rubyconf; public class Car extends Vehicle { public void

    move() { System.out.println("Moving..."); } }
  16. Contrato informal: é preciso que a classe que inclui o

    module Enumerable defina um método each
  17. class Library include Enumerable def initialize @books = [] end

    def add_book(book) @books << book end def each @books.each { |book| yield book } end end
  18. library = Library.new library.add_book Book.new("Book 1") library.add_book Book.new("Book 2") library.add_book

    Book.new("Book 3") library.each { |book| puts book.title } # Book 1 # Book 2 # Book 3
  19. C++

  20. class Tax { public: float virtual dueValue() = 0; float

    virtual retainedValue() = 0; string virtual getName() = 0; Tax(float _value) {} protected: float value; };
  21. class Irpj : public Tax { public: Irpj(float _value) :

    Tax(_value) { this->value = _value; } float dueValue() { return value * 0.033; } float retainedValue() { return value * 0.015; } string getName() { return "IRPJ"; } };
  22. class Pis : public Tax { public: Pis(float _value) :

    Tax(_value) { this->value = _value; } float dueValue() { return 0.0; } float retainedValue() { return value * 0.0065; } string getName() { return "PIS"; } };
  23. class Invoice { public: Invoice(float _value) { value = _value;

    Irpj *irpj = new Irpj(value); Pis *pis = new Pis(value); taxes.push_back(irpj); taxes.push_back(pis); } void print() { for (unsigned int i = 0; i < taxes.size(); i++) { Tax *tax = taxes[i]; cout << tax->getName() << endl; cout << "Devido: R$" << tax->dueValue() << endl; cout << "Retido: R$" << tax->retainedValue() << endl; } } private: float value; vector<Tax*> taxes; };
  24. int main (int argc, char const* argv[]) { Invoice invoice

    = Invoice(1000.00); invoice.print(); return 0; } // IRPJ // Devido: R$33 // Retido: R$15 // PIS // Devido: R$0 // Retido: R$6.5
  25. public class Irpj implements Tax { private double value; public

    Irpj(double value) { this.value = value; } public double dueValue() { return value * 0.033; } public double retainedValue() { return value * 0.015; } public String getName() { return "IRPJ"; } }
  26. public class Pis implements Tax { private double value; public

    Pis(double value) { this.value = value; } public double dueValue() { return 0.0; } public double retainedValue() { return value * 0.0065; } public String getName() { return "PIS"; } }
  27. public class Invoice { private List<Tax> taxes = new ArrayList<Tax>();

    private double value; public Invoice(double value) { this.value = value; Irpj irpj = new Irpj(this.value); Pis pis = new Pis(this.value); taxes.add(irpj); taxes.add(pis); } public void print() { for(Tax tax : taxes) { System.out.println(tax.getName()); System.out.println("Devido: R$" + tax.dueValue()); System.out.println("Retido: R$" + tax.retainedValue()); } } }
  28. package br.com.rubyconf; public class Main { public static void main(String[]

    args) { Invoice invoice = new Invoice(1000.00); invoice.print(); } } //IRPJ //Devido: R$33.0 //Retido: R$15.0 //PIS //Devido: R$0.0 //Retido: R$6.5
  29. class Irpj include Tax def name "IRPJ" end def retained_value

    value * 0.015 end def due_value value * 0.033 end end
  30. class Pis include Tax def name "PIS" end def retained_value

    value * 0.0065 end def due_value 0.0 end end
  31. class Invoice def initialize(value) @value = value @taxes = []

    @taxes << Irpj.new(value) @taxes << Pis.new(value) end def print @taxes.each do |tax| puts tax.name puts "Devido: R$#{tax.due_value}" puts "Retido: R$#{tax.retained_value}" end end end
  32. invoice = Invoice.new(1000.0) invoice.print # IRPJ # Devido: R$33.0 #

    Retido: R$15.0 # PIS # Devido: R$0.0 # Retido: R$6.5
  33. C++

  34. class Printer { public: void print(Report report) { // ...

    } void print(Note note) { // ... } void print(Document document) { // ... } };
  35. public class Printer { public void print(Document document) { //

    ... } public void print(Note note) { // ... } public void print(Report report) { // ... } }
  36. class Printer def print(printable) case printable when Document print_document printable

    when Note print_note printable when Report print_report printable end end private def print_document(printable) # ... end def print_note(printable) # ... end def print_report(printable) # ... end end
  37. C++

  38. template <class Printable> class Printer { public: void print(Printable printable)

    { cout << "Printing a " << typeid(printable).name() << endl; } };
  39. int main (int argc, char const* argv[]) { Printer<Note> printer

    = Printer<Note>(); printer.print(Note()); return 0; }
  40. public class Main { public static void main(String[] args) {

    Printer<Document> printer = new Printer<Document>(); printer.print(new Document()); } }
  41. C++

  42. template <class Printable> class Printer { public: Printer() { printables

    = vector<Printable>(); } void print(Printable printable) { cout << "Printing a " << typeid(printable).name() << endl; } void addPrintable(Printable printable) { printables.push_back(printable); } void printAll() { for (int i = 0; i < printables.size(); i++) { print(printables[i]); } } private: vector<Printable> printables; };
  43. public class Printer<Printable> { private List<Printable> printables = new ArrayList<Printable>();

    public void addPrintable(Printable printable) { printables.add(printable); } public void print(Printable document) { System.out.println("Printing a " + document); } public void printAll() { for(Printable printable : printables) { print(printable); } } }
  44. public class Main { public static void main(String[] args) {

    Printer<Document> printer = new Printer<Document>(); Document doc1 = new Document(); Document doc2 = new Document(); printer.addPrintable(doc1); printer.addPrintable(doc2); printer.printAll(); } }
  45. class Printer def initialize @printables = [] end def add_printable(printable)

    @printables << printable end def print(printable) puts "Printing a #{printable.class.name}..." end def print_all @printables.each { |p| print p } end end
  46. printer = Printer.new doc1 = Document.new printer.add_printable doc1 doc2 =

    Document.new printer.add_printable doc2 printer.print_all
  47. printer = Printer.new doc = Document.new printer.add_printable doc1 note =

    Note.new printer.add_printable note report = Report.new printer.add_printable report foo = Foobar.new printer.add_printable foo printer.print_all
  48. C++

  49. class TotalCalculatorWithDiscount : public TotalCalculator { private: double discountPercentage; public:

    TotalCalculatorWithDiscount(double discountPercentage) { this->discountPercentage = discountPercentage; } double total(vector<LineItem> items) { double t = 0.0; for (unsigned int i = 0; i < items.size(); i++) { t += items[i].getTotal(); } return t - (t * discountPercentage/100); } };
  50. class Cart { private: vector<LineItem> items; TotalCalculator *calculator; public: Cart(TotalCalculator

    *calculator) { this->calculator = calculator; } vector<LineItem> getItems() { return items; } double getTotal(); }; double Cart::getTotal() { return calculator->total(); }
  51. TEST(Cart, ReturnsTotalValue) { MockTotalCalculator calculator; LineItem lineItem1 = LineItem(10.0, 2);

    LineItem lineItem2 = LineItem(15.0, 3); Cart cart = Cart(calculator); cart.addItem(lineItem1); cart.addItem(lineItem2); vector<LineItem> items; items.push_back(line_item1); items.push_back(line_item2); EXPECT_CALL(calculator, total(items)) .WillOnce(Return(65.00)); EXPECT_EQ(cart.getTotal(), 65.00); }
  52. public class TotalCalculatorWithDiscount implements TotalCalculator { private double percentageDiscount; public

    TotalCalculatorWithDiscount(double percentageDiscount) { this.percentageDiscount = percentageDiscount; } public double total(List<LineItem> items) { double t = 0.0; for(LineItem item : items) { t += item.getTotal(); } return t - (t * percentageDiscount/100.0); } }
  53. public class Cart { private List<LineItem> items = new ArrayList<LineItem>();

    private TotalCalculator calculator; public Cart(TotalCalculator calculator) { this.calculator = calculator; } public void addItem(LineItem item) { items.add(item); } public double getTotal() { return calculator.total(items); } }
  54. import static org.mockito.Mockito.*; public class TestCart { @Test public void

    calculatesTotalValue() { LineItem item1 = mock(LineItem.class); LineItem item2 = mock(LineItem.class); List<LineItem> items = new ArrayList<LineItem>(); TotalCalculator mockedCalculator = mock(TotalCalculator.class); items.add(item1); items.add(item2); when(mockedCalculator.total(items)).thenReturn(65.00); Cart cart = new Cart(mockedCalculator); cart.addItem(item1); cart.addItem(item2); assertEquals(cart.getTotal(), 65.00, 0.0001); verify(mockedCalculator).total(items); } }
  55. class TotalCalculatorWithDiscount def initialize(percentage_discount) @percentage_discount = percentage_discount end def total(items)

    t = items.inject(0.0) { |total, item| total += item.total } t - (t * percentage_discount / 100.0) end end
  56. class Cart attr_reader :items def initialize(calculator) @items = [] @calculator

    = calculator end def add_item(item) @items << item end def total @calculator.total items end end
  57. describe Cart do describe "#total" do it "calculates the cart's

    total" do calculator = stub item1 = stub item2 = stub calculator.should_receive(:total) .with([item1, item2]).and_return(65.00) cart = Cart.new calculator cart.add_item item1 cart.add_item item2 cart.total.should == 65.00 end end end
  58. Se você sabe o tipo, você sabe a quais contratos

    o objeto atende (quais métodos são implementados)
  59. ?