I have this code: Show
Then i Have another class which extends Base, for instance:
which also happens to have method delete. Here comes the problem: When i call
I get the:
So my question is, why i can't have the method of descendant with different parameters? Thank you for explaining. asked Jul 24, 2013 at 15:21
Martin SvobodaMartin Svoboda 2781 gold badge3 silver badges16 bronze badges This is because PHP does method overriding not method overloading. So method signatures must match exactly. As a work arround for your issue you can restructure delete on your base class to
Then change your subclasses method signature to match. answered Jul 24, 2013 at 15:27
1 To override the function in the base class, a method must have the identical "Signature" to the one it is displacing. A signature consists of the name, the parameters (and parameter order), and the return type. This is the essence of polymorphism, and is where object-oriented programming gains much of its power. If you don't need to override the parent's methods, give your new method a different name.
codingbiz 25.8k8 gold badges55 silver badges93 bronze badges answered Jul 24, 2013 at 15:26
CurtCurt 5,3881 gold badge20 silver badges35 bronze badges 1 This is suposed to be a comment to @orangePill's ansert, but I don't have reputation enough to comment. I had this same issue with static methods, and I did the following, using late static binding. Perhaps it helps someone.
Usage
answered Jul 23, 2014 at 18:13
QuiquetasQuiquetas 2885 silver badges9 bronze badges Method overriding, in object-oriented programming, is a language feature that allows a subclass or child class to provide a specific implementation of a method that is already provided by one of its superclasses or parent classes. It allows for a specific type of polymorphism (subtyping). The implementation in the subclass overrides (replaces) the implementation in the superclass by providing a method that has same name, same parameters or signature, and same return type as the method in the parent class.[1] The version of a method that is executed will be determined by the object that is used to invoke it. If an object of a parent class is used to invoke the method, then the version in the parent class will be executed, but if an object of the subclass is used to invoke the method, then the version in the child class will be executed.[2] Some languages allow a programmer to prevent a method from being overridden. Language-specific examples[edit]Ada[edit]Ada provides method overriding by default. To favor early error detection (e.g. a misspelling), it is possible to specify when a method is expected to be actually overriding, or not. That will be checked by the compiler. type T is new Controlled with ......; procedure Op(Obj: in out T; Data: in Integer); type NT is new T with null record; overriding -- overriding indicator procedure Op(Obj: in out NT; Data: in Integer); overriding -- overriding indicator procedure Op(Obj: in out NT; Data: in String); -- ^ compiler issues an error: subprogram "Op" is not overriding C#[edit]C# does support method overriding, but only if explicitly requested using the modifiers abstract class Animal { public string Name { get; set; } // Methods public void Drink(); public virtual void Eat(); public void Go(); } class Cat : Animal { public new string Name { get; set; } // Methods public void Drink(); // Warning: hides inherited drink(). Use new public override void Eat(); // Overrides inherited eat(). public new void Go(); // Hides inherited go(). } When overriding one method with another, the signatures of the two methods must be identical (and with same visibility). In C#, class methods, indexers, properties and events can all be overridden. Non-virtual or static methods cannot be overridden. The overridden base method must be virtual, abstract, or override. In addition to the modifiers that are used for method overriding, C# allows the hiding of an inherited property or method. This is done using the same signature of a property or
method but adding the modifier In the above example, hiding causes the following: Cat cat = new Cat(); cat.Name = …; // accesses Cat.Name cat.Eat(); // calls Cat.Eat() cat.Go(); // calls Cat.Go() ((Animal)cat).Name = …; // accesses Animal.Name! ((Animal)cat).Eat(); // calls Cat.Eat()! ((Animal)cat).Go(); // calls Animal.Go()! C++[edit]C++ does not have the keyword #include <iostream> //--------------------------------------------------------------------------- class Rectangle { public: Rectangle(double l, double w) : length_(l), width_(w) {} virtual void Print() const; private: double length_; double width_; }; //--------------------------------------------------------------------------- void Rectangle::Print() const { // Print method of base class. std::cout << "Length = " << length_ << "; Width = " << width_; } //--------------------------------------------------------------------------- class Box : public Rectangle { public: Box(double l, double w, double h) : Rectangle(l, w), height_(h) {} void Print() const override; private: double height_; }; //--------------------------------------------------------------------------- // Print method of derived class. void Box::Print() const { // Invoke parent Print method. Rectangle::Print(); std::cout << "; Height = " << height_; } The method The following statements will instantiate objects of type int main(int argc, char** argv) { Rectangle rectangle(5.0, 3.0); // Outputs: Length = 5.0; Width = 3.0 rectangle.Print(); Box box(6.0, 5.0, 4.0); // The pointer to the most overridden method in the vtable in on Box::print, // but this call does not illustrate overriding. box.Print(); // This call illustrates overriding. // outputs: Length = 6.0; Width = 5.0; Height= 4.0 static_cast<Rectangle&>(box).Print(); } In
C++11, similar to Java, a method that is declared Delphi[edit]In Delphi, method overriding is done with the directive override, but only if a method was marked with the dynamic or virtual directives. The inherited reserved word must be called when you want to call super-class behavior type TRectangle = class private FLength: Double; FWidth: Double; public property Length read FLength write FLength; property Width read FWidth write FWidth; procedure Print; virtual; end; TBox = class(TRectangle) public procedure Print; override; end; Eiffel[edit]In Eiffel, feature redefinition is analogous to method overriding in C++ and Java. Redefinition is one of three forms of feature adaptation classified as redeclaration. Redeclaration also covers effecting, in which an implementation is provided for a feature which was deferred (abstract) in the parent class, and undefinition, in which a feature that was effective (concrete) in the parent becomes deferred again in the heir class. When a feature is redefined, the feature name is kept by the heir class, but properties of the feature such as its signature, contract (respecting restrictions for preconditions and postconditions), and/or implementation will be different in the heir. If the original feature in the parent class, called the heir feature's precursor, is effective, then the redefined feature in the heir will be effective. If the precursor is deferred, the feature in the heir will be deferred.[5] The intent to redefine a feature, as class THOUGHT feature message -- Display thought message do print ("I feel like I am diagonally parked in a parallel universe.%N") end end class ADVICE inherit THOUGHT redefine message end feature message -- Precursor do print ("Warning: Dates in calendar are closer than they appear.%N") end end In class Consider a class which uses instances for both class APPLICATION create make feature make -- Run application. do (create {THOUGHT}).message; (create {ADVICE}).message end end When instantiated, class I feel like I am diagonally parked in a parallel universe. Warning: Dates in calendar are closer than they appear. Within a redefined feature, access to the feature's precursor can be gained by using
the language keyword message -- Precursor do print ("Warning: Dates in calendar are closer than they appear.%N") Precursor end Invocation of the feature now includes the execution of Warning: Dates in calendar are closer than they appear. I feel like I am diagonally parked in a parallel universe. Java[edit]In
Java, when a subclass contains a method that overrides a method of the superclass, it can also invoke the superclass method by using the keyword
class Thought { public void message() { System.out.println("I feel like I am diagonally parked in a parallel universe."); } } public class Advice extends Thought { @Override // @Override annotation in Java 5 is optional but helpful. public void message() { System.out.println("Warning: Dates in calendar are closer than they appear."); } } Class Thought parking = new Thought(); parking.message(); // Prints "I feel like I am diagonally parked in a parallel universe." Thought dates = new Advice(); // Polymorphism dates.message(); // Prints "Warning: Dates in calendar are closer than they appear." The public class Advice extends Thought { @Override public void message() { System.out.println("Warning: Dates in calendar are closer than they appear."); super.message(); // Invoke parent's version of method. } There are methods that a subclass cannot override. For example, in Java, a method that is declared final in the super class cannot be overridden. Methods that are declared private or static cannot be overridden either because they are implicitly final. It is also impossible for a class that is declared final to become a super class.[6] Kotlin[edit]In
Kotlin we can simply override a function like this (note that the function must be fun main() { val p = Parent(5) val c = Child(6) p.myFun() c.myFun() } open class Parent(val a : Int) { open fun myFun() = println(a) } class Child(val b : Int) : Parent(b) { override fun myFun() = println("overrided method") } Python[edit]In
Python, when a subclass contains a method that overrides a method of the superclass, you can also call the superclass method by calling class Thought: def __init__(self) -> None: print("I'm a new object of type Thought!") def message(self) -> None: print("I feel like I am diagonally parked in a parallel universe.") class Advice(Thought): def __init__(self) -> None: super(Advice, self).__init__() def message(self) -> None: print("Warning: Dates in calendar are closer than they appear") super(Advice, self).message() t = Thought() # "I'm a new object of type Thought!" t.message() # "I feel like I am diagonally parked in a parallel universe. a = Advice() # "I'm a new object of type Thought!" a.message() # "Warning: Dates in calendar are closer than they appear" # "I feel like I am diagonally parked in a parallel universe. # ------------------ # Introspection: isinstance(t, Thought) # True isinstance(a, Advice) # True isinstance(a, Thought) # True Ruby[edit]In Ruby when a subclass contains a method that overrides a method of the superclass, you can also call the superclass method by calling super in that overridden method. You can use alias if you would like to keep the overridden method available outside of the overriding method as shown with 'super_message' below. Example: class Thought def message puts "I feel like I am diagonally parked in a parallel universe." end end class Advice < Thought alias :super_message :message def message puts "Warning: Dates in calendar are closer than they appear" super end end Notes[edit]
See also[edit]
References[edit]
External links[edit]
When a method has the same name and takes the same parameters?Overloading happens when you have two methods with the same name but different signatures (or arguments). In a class we can implement two or more methods with the same name. Overloaded methods are differentiated based on the number and type of parameter passed as arguments to the methods.
What is it called when two methods have the same name but different parameters?The practice of defining two or more methods within the same class that share the same name but have different parameters is called overloading methods.
Can you define two methods in the same class with the same name and parameter list?You cannot declare more than one method with the same name and the same number and type of arguments, because the compiler cannot tell them apart. The compiler does not consider return type when differentiating methods, so you cannot declare two methods with the same signature even if they have a different return type.
What happened if two methods have same name same parameters but different return types?The compiler does not consider the return type while differentiating the overloaded method. But you cannot declare two methods with the same signature and different return types. It will throw a compile-time error. If both methods have the same parameter types, but different return types, then it is not possible.
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