Classes

Visão Geral

The 4D language supports the concept of classes. Numa linguagem de programação, a utilização de uma classe permite definir um comportamento do objecto com propriedades e funções associadas.

Once a user class is defined, you can instantiate objects of this class anywhere in your code. Cada objecto é uma instância da sua classe. A class can extend another class, and then inherits from its functions and properties (declared and computed).

O modelo de classe em 4D é semelhante às classes em JavaScript, e baseado numa cadeia de protótipos.

For example, you could create a Person class with the following definition:

//Class: Person.4dm
Class constructor($firstname : Text; $lastname : Text)
 This.firstName:=$firstname
 This.lastName:=$lastname

Function get fullName() -> $fullName : Text
 $fullName:=This.firstName+" "+This.lastName

Function sayHello() -> $welcome : Text

 $welcome:="Hello "+This.fullName

Ou em um método, criar uma "Pessoa":

var $person : cs. Person //object of Person class  
var $hello : Text
$person:=cs. Person.new("John";"Doe")
// $person:{firstName: "John"; lastName: "Doe" }
$hello:=$person.sayHello() //"Hello John Doe"

Gestão de classes

Definição de classe

A user class in 4D is defined by a specific method file (.4dm), stored in the /Project/Sources/Classes/ folder. O nome do arquivo é o nome da classe.

Ao nomear classes, deve ter em mente as seguintes regras:

• A class name must be compliant with property naming rules.
• Nomes de classe diferenciam minúsculas de maiúsculas.
• Não se recomenda dar o mesmo nome a uma classe e a uma tabela de base de dados, a fim de evitar qualquer conflito.

Por exemplo, se quiser definir uma classe chamada "Polígono", precisa criar o seguinte arquivo:

Project folder

Eliminação de uma classe

Para eliminar uma classe existente, pode:

• no seu disco, remover o arquivo de classe .4dm da pasta "Classes",
• in the 4D Explorer, select the class and click or choose Move to Trash from the contextual menu.

Using 4D interface

Class files are automatically stored at the appropriate location when created through the 4D interface, either via the File menu or the Explorer.

Menu Arquivo e barra de ferramentas

You can create a new class file for the project by selecting New > Class... in the 4D Developer File menu or from the toolbar.

You can also use the Ctrl+Shift+Alt+k shortcut.

Explorador

In the Methods page of the Explorer, classes are grouped in the Classes category.

Para criar uma nova classe, pode:

• select the Classes category and click on the button.
• select New Class... from the action menu at the bottom of the Explorer window, or from the contexual menu of the Classes group.
• select New > Class... from the contexual menu of the Explorer's Home page.

Suporte de código de classe

Nas várias janelas 4D (editor de código, compilador, depurador, explorador de tempo de execução), o código de classe é basicamente tratado como um método de projecto com algumas especificidades:

• No editor de código:
  • uma aula não pode ser executada
  • uma função de classe é um bloco de código
  • Goto definition on an object member searches for class Function declarations; for example, "$o.f()" will find "Function f".
  • Search references on class function declaration searches for the function used as object member; for example, "Function f" will find "$o.f()".
• In the Runtime explorer and Debugger, class functions are displayed with the <ClassName> constructor or <ClassName>.<FunctionName> format.

Lojas de classe

As classes disponíveis são acessíveis a partir das suas class stores. Estão disponíveis duas class stores:

• cs for user class store
• 4D for built-in class store

cs

cs : Object

Parâmetro	Tipo		Descrição
classStore	Object	<-	Class store de usuário para o projeto ou componente

The cs command returns the user class store for the current project or component. It returns all user classes defined in the opened project or component. By default, only project ORDA classes are available.

Exemplo

You want to create a new instance of an object of myClass:

$instance:=cs.myClass.new()

4D

4D : Object

Parâmetro	Tipo		Descrição
classStore	Object	<-	Class store 4D

The 4D command returns the class store for available built-in 4D classes. It provides access to specific APIs such as CryptoKey.

Exemplo

You want to create a new key in the CryptoKey class:

$key:=4D. CryptoKey.new(New object("type";"ECDSA";"curve";"prime256v1"))

Objecto de classe

When a class is defined in the project, it is loaded in the 4D language environment. A class is an object itself, of "Class" class. Um objecto classe tem as seguintes propriedades e função:

• name string
• superclass object (null if none)
• new() function, allowing to instantiate class objects
• isShared property, true if the class is shared
• isSingleton property, true if the class defines a singleton.
• me property, allowing to instantiate and access singletons.

In addition, a class object can reference a constructor object (optional).

A class object itself is a shared object and can therefore be accessed from different 4D processes simultaneously.

Herança

If a class inherits from another class (i.e. the Class extends keyword is used in its definition), the parent class is its superclass.

When 4D does not find a function or a property in a class, it searches it in its superclass; if not found, 4D continues searching in the superclass of the superclass, and so on until there is no more superclass (all objects inherit from the "Object" superclass).

Palavras-chave de classe

As palavras-chave 4D específicas podem ser utilizadas nas definições de classes:

• Function <Name> to define class functions of the objects.
• Class constructor to initialize new objects of the class.
• property to define static properties of the objects with a type.
• Function get <Name> and Function set <Name> to define computed properties of the objects.
• Class extends <ClassName> to define inheritance.

Function

Sintaxe

{shared} Function <name>({$parameterName : type; ...}){->$parameterName : type}
// code

As funções de classe são propriedades específicas da classe. They are objects of the 4D.Function class. In the class definition file, function declarations use the Function keyword followed by the function name.

If the function is declared in a shared class, you can use the shared keyword so that the function could be called without Use...End use structure. For more information, refer to the Shared functions paragraph below.

The function name must be compliant with object naming rules.

nota

Como propriedades e funções compartilham o mesmo espaço de nomes, usar o mesmo nome para uma propriedade e uma função da mesma classe não é permitido (um erro é lançado nesse caso).

tip

Dica: Começar o nome da função com um caractere de sublinhado ("_") excluirá a função dos recursos de preenchimento automático no editor de código 4D. For example, if you declare `Function _myPrivateFunction` in `MyClass`, it will not be proposed in the code editor when you type in `"cs.MyClass. "`.

Immediately following the function name, parameters for the function can be declared with an assigned name and data type, including the return parameter (optional). Por exemplo:

Function computeArea($width : Integer; $height : Integer)->$area : Integer

Within a class function, the This command is used as the object instance. Por exemplo:

Function setFullname($firstname : Text; $lastname : Text)
 This.firstName:=$firstname
 This.lastName:=$lastname

Function getFullname()->$fullname : Text
 $fullname:=This.firstName+" "+Uppercase(This.lastName)

For a class function, the Current method name command returns: <ClassName>.<FunctionName>, for example "MyClass.myFunction".

In the application code, class functions are called as member methods of the object instance and can receive parameters if any. As seguintes sintaxes são suportadas:

• use of the () operator. For example, myObject.methodName("hello")
• use of a "4D. Function" class member method:
  • apply()
  • call()

Thread-safety warning

Se uma função de classe não for thread-safe e for chamada por um método com o atributo "Pode ser executado num processo preemptivo":

• o compilador não gera qualquer erro (o que é diferente dos métodos normais),
• um erro é lançado por 4D apenas em tempo de execução.

Parâmetros

Os parâmetros da função são declarados utilizando o nome do parâmetro e o tipo de parâmetro, separados por dois pontos. The parameter name must be compliant with property naming rules. Os parâmetros (e tipos) múltiplos são separados por ponto e vírgula (;).

Function add($x; $y : Variant; $z : Integer; $xy : Object)

nota

If the type is not stated, the parameter will be defined as Variant.

Valor retornado

You declare the return parameter (optional) by adding an arrow (->) and the return parameter definition after the input parameter(s) list, or a colon (:) and the return parameter type only. Por exemplo:

Function add($x : Variant; $y : Integer)->$result : Integer
 $result:=$x+$y

You can also declare the return parameter by adding only : type and use the return expression (it will also end the function execution). Por exemplo:

Function add($x : Variant; $y : Integer)->$result : Integer

Exemplo 1

property name : Text
property height; width : Integer

// Class: Rectangle
Class constructor($width : Integer; $height : Integer)
 This.name:="Rectangle"
 This.height:=$height
 This.width:=$width

// Function definition
Function getArea()->$result : Integer
 $result:=(This.height)*(This.width)

// In a project method

var $rect : cs. Rectangle
var $area : Real

$rect:=cs. Rectangle.new(50;100)  
$area:=$rect.getArea() //5000

Exemplo 2

This example uses the return expression:

Function getRectArea($width : Integer; $height : Integer) : Integer
 If ($width > 0 && $height > 0)
  return $width * $height
 Else
  return 0
 End if

Class constructor

Sintaxe

// Class: MyClass
{shared} {singleton} Class Constructor({$parameterName : type; ...})
// code

A class constructor function accepts optional parameters and can be used to create and initialize objects of the user class.

When you call the new() function, the class constructor is called with the parameters optionally passed to the new() function.

Só pode haver uma função de construtor em uma classe (caso contrário um erro é retornado). A constructor can use the Super keyword to call the constructor of the super class.

É possível criar e digitar propriedades de instância dentro do construtor (ver exemplo). Alternatively, if your instance properties' values do not depend on parameters passed to the constructor, you can define them using the property keyword.

Using the shared keyword creates a shared class, used to only instantiate shared objects. For more information, refer to the Shared classes paragraph.

Using the singleton keyword creates a singleton, used to create a single instance. For more information, refer to the Singleton classes paragraph.

Exemplo

// Class: MyClass
// Class constructor of MyClass Class Constructor ($name : Text)
 This.name:=$name

// In a project method
// You can instantiate an object
var $o : cs. MyClass
$o:=cs. MyClass.new("HelloWorld")  
// $o = {"name":"HelloWorld"}

propriedade

Sintaxe

property <propertyName>{; <propertyName2>;...}{ : <propertyType>}

The property keyword can be used to declare a property inside a user class. Uma propriedade de classe tem um nome e um tipo.

A declaração de propriedades de classe melhora as sugestões do editor de código, as funcionalidades de antecipação de tipos e a detecção de erros.

Properties are declared for new objects when you call the new() function, however they are not automatically added to objects (they are only added when they are assigned a value).

nota

A property is automatically added to the object when it is inititalized in the declaration line.

Property names must be compliant with property naming rules.

nota

Como propriedades e funções compartilham o mesmo espaço de nomes, usar o mesmo nome para uma propriedade e uma função da mesma classe não é permitido (um erro é lançado nesse caso).

O tipo de propriedade pode ser um dos seguintes tipos suportados:

Sintaxe	Conteúdos
Text	Valor texto
Date	Valor data
Time	Valor Hora
Boolean	Valor booleano
Integer	Valor inteiro longo
Real	Valor real
Pointer	Valor ponteiro
Picture	Valor imagem
Blob	Valor BLOB
Collection	Valor colecção
Variant	Valor variant
Object	Object with default class (4D.Object)
4D.<className>	Objecto do nome da classe 4D
cs.<className>	Objeto do nome da classe usuário
cs.<namespace>.<className>	Objeto do nome da classe do componente <namespace>

Se você omitir o tipo na linha de declaração, a propriedade é criada como uma variante.

info

The property keyword can only be used in class methods and outside any Function or Class Constructor block.

Inicializando a propriedade na linha de declaração

Ao declarar uma propriedade, você tem a flexibilidade de especificar seu tipo de dados e fornecer seu valor em uma única instrução. A sintaxe suportada é:

property <propertyName> { : <propertyType>} := <Propertyvalue>

nota

Ao usar essa sintaxe, você não pode declarar várias propriedades na linha de declaração.

Você pode omitir o tipo na linha da declaração, caso em que o tipo será inferido quando possível. Por exemplo:

// Class: MyClass

property name : Text := "Smith"
property age : Integer := 42

property birthDate := !1988-09-29! //date is inferred
property fuzzy //variant

When you initialize a property in its declaration line, it is added to the class object after its instantiation with the new() function but before the constructor is called.

If a class extends another class, the properties of the parent class are instantiated before the properties of the child class.

Exemplo

// Class: MyClass

property name : Text
property age : Integer
property color : Text := "Blue"

Num método:

var $o : cs.MyClass
$o:=cs.MyClass.new() //$o:{"color" : "Blue"}
$o.name:="John" //$o:{"color" : "Blue"; "name" : "John"}
$o.age:="Smith"  //error com a sintaxe checada

Function get and Function set

Sintaxe

{shared} Function get <name>()->$result : type
// code

{shared} Function set <name>($parameterName : type)
// código

Function get and Function set are accessors defining computed properties in the class. Uma propriedade calculada é uma propriedade nomeada com um tipo de dados que oculta um cálculo. Quando um valor de propriedade computado é acessado, 4D substitui o código do acessor correspondente:

• when the property is read, the Function get is executed,
• when the property is written, the Function set is executed.

Se a propriedade não for acedida, o código nunca é executado.

As propriedades computadas são concebidas para tratar dados que não precisam de ser guardados na memória. São geralmente baseados em propriedades persistentes. For example, if a class object contains as persistent property the gross price and the VAT rate, the net price could be handled by a computed property.

In the class definition file, computed property declarations use the Function get (the getter) and Function set (the setter) keywords, followed by the name of the property. The name must be compliant with property naming rules.

Function get returns a value of the property type and Function set takes a parameter of the property type. Both arguments must comply with standard function parameters.

When both functions are defined, the computed property is read-write. If only a Function get is defined, the computed property is read-only. Neste caso, é devolvido um erro se o código tentar modificar a propriedade. If only a Function set is defined, 4D returns undefined when the property is read.

If the functions are declared in a shared class, you can use the shared keyword with them so that they could be called without Use...End use structure. For more information, refer to the Shared functions paragraph below.

The type of the computed property is defined by the $return type declaration of the getter. It can be of any valid property type.

Assigning undefined to an object property clears its value while preserving its type. In order to do that, the Function get is first called to retrieve the value type, then the Function set is called with an empty value of that type.

Exemplo 1

//Class: Person.4dm
property firstName; lastName : Text

Class constructor($firstname : Text; $lastname : Text)
 This.firstName:=$firstname
 This.lastName:=$lastname

Function get fullName() -> $fullName : Text
 $fullName:=This.firstName+" "+This.lastName

Function set fullName( $fullName : Text )
 $p:=Position(" "; $fullName)
 This.firstName:=Substring($fullName; 1; $p-1)
 This.lastName:=Substring($fullName; $p+1)

//num método projecto
$fullName:=$person.fullName // A função get fullName() é chamada
$person.fullName:="John Smith" // A função set fullName() é chamada

Exemplo 2

Function get fullAddress()->$result : Object

 $result:=New object

 $result.fullName:=This.fullName
 $result.address:=This.address
 $result.zipCode:=This.zipCode
 $result.city:=This.city
 $result.state:=This.state
 $result.country:=This.country

Class extends <ClassName>

Sintaxe

// Class: ChildClass
Class extends <ParentClass>

The Class extends keyword is used in class declaration to create a user class which is a child of another user class. A classe filha herda todas as funções da classe mãe.

A extensão de classe deve respeitar as seguintes regras:

• A user class cannot extend a built-in class (except 4D.Object and ORDA classes which are extended by default for user classes).
• Uma classe de usuário não pode estender uma classe de usuário de outro projeto ou componente.
• Uma classe usuário não se pode estender a si própria.
• Não é possível estender classes de forma circular (ou seja, "a" estende "b" que estende "a").
• It is not possible to define a shared user class extended from a non-shared user class.

Breaking such a rule is not detected by the code editor or the interpreter, only the compiler and check syntax will throw an error in this case.

An extended class can call the constructor of its parent class using the Super command.

Exemplo

This example creates a class called Square from a class called Polygon.

//Class: Square

//path: Classes/Square.4dm

Class extends Polygon

Class constructor ($side : Integer)

 // It calls the parent class's constructor with lengths
 // provided for the Polygon's width and height
 Super($side;$side)
 // In derived classes, Super must be called before you
 // can use 'This'
 This.name:="Square"



 Function getArea() -> $area : Integer
  $area:=This.height*This.width

Super

Super( ...param : any )
Super : Object

Parâmetro	Tipo		Descrição
param	any	->	Parâmetro(s) a passar para o construtor pai
Resultados	Object	<-	Pai do objecto

The Super keyword allows calls to the superclass, i.e. the parent class.

Super serves two different purposes:

1. Inside a constructor code, Super is a command that allows to call the constructor of the superclass. When used in a constructor, the Super command appears alone and must be used before the This keyword is used.

• Se todos os construtores de classe na árvore de herança não forem correctamente chamados, é gerado o erro -10748. É o programador 4D que se certifica de que as chamadas são válidas.
• If the This command is called on an object whose superclasses have not been constructed, error -10743 is generated.
• If Super is called out of an object scope, or on an object whose superclass constructor has already been called, error -10746 is generated.

// dentro do construtor myClass
var $text1; $text2 : Text
Super($text1) //chama o construtor da superclasse com um parâmetro de texto
This.param:=$text2 // usa o segundo parâmetro

2. Inside a class member function, Super designates the prototype of the superclass and allows to call a function of the superclass hierarchy.

Super.doSomething(42) //chamada a função "doSomething"  
//declarada em superclasses

Exemplo 1

This example illustrates the use of Super in a class constructor. The command is called to avoid duplicating the constructor parts that are common between Rectangle and Square classes.

// Class: Rectangle
Class constructor($width : Integer; $height : Integer)
 This.name:="Rectangle"
 This.height:=$height
 This.width:=$width


Function sayName()
 ALERT("Hi, I am a "+This.name+".")

// Function definition
Function getArea()
 var $0 : Integer

 $0:=(This.height)*(This.width)

//Classe: Square

Classe extends Rectangle

Construtor da classe ($side : Integer)

 // Chama o construtor da classe pai com comprimentos
 // fornecidos para a largura e altura do Rectangle
 Super($side;$side)
 // Em classes derivadas, Super tem de ser chamado antes de
 // poder usar 'This'
 This.name:="Square"

Function getArea()
 C_LONGINT($0)
 $0:=This.height*This.width

Exemplo 2

This example illustrates the use of Super in a class member method. You created the Rectangle class with a function:

//Classe: Rectângulo

Function nbSides()
 var $0 : Text
 $0:="I have 4 sides"

You also created the Square class with a function calling the superclass function:

//Classe: Quadrado

Class extends Rectangle

Function description()
 var $0 : Text
 $0:=Super.nbSides()+" que são todos iguais"

Depois pode escrever num método projecto:

Parâmetros

This

This : Object

Parâmetro	Tipo		Descrição
Resultados	Object	<-	Objecto actual

The This keyword returns a reference to the currently processed object.

In most cases, the value of This is determined by how a function is called. Não pode ser definido por atribuição durante a execução e pode ser diferente de cada vez que a função é chamada.

When a formula is called as a member method of an object, its This is set to the object the method is called on. Por exemplo:

$o:=New object("prop";42;"f";Formula(This.prop))
$val:=$o.f() //42

When a class constructor function is used (with the new() function), its This is bound to the new object being constructed.

//Class: ob Class Constructor  

 // Create properties on This as
 // desired by assigning to them
 This.a:=42

// num método 4D  
$o:=cs.ob.new()
$val:=$o.a //42

When calling the superclass constructor in a constructor using the Super keyword, keep in mind that This must not be called before the superclass constructor, otherwise an error is generated. See this example.

In any cases, This refers to the object the method was called on, as if the method were on the object.

//Class: ob Function f()
 $0:=This.a+This.b

Depois pode escrever num método projecto:

$o:=cs.ob.new()
$o.a:=5
$o.b:=3
$val:=$o.f() //8

In this example, the object assigned to the variable $o doesn't have its own f property, it inherits it from its class. Since f is called as a method of $o, its This refers to $o.

Comandos de classe

Vários comandos da linguagem 4D permitem-lhe lidar com funcionalidades de classe.

OB Class

OB Class ( object ) -> Object | Null

OB Class returns the class of the object passed in parameter.

OB Instance of

OB Instance of ( object ; class ) -> Boolean

OB Instance of returns true if object belongs to class or to one of its inherited classes, and false otherwise.

Classes compartilhadas

You can create shared classes. A shared class is a user class that instantiates a shared object when the new() function is called on the class. Uma classe compartilhada só pode criar objetos compartilhados.

Shared classes also support shared functions that can be called without Use...End use structures.

The .isShared property of Class objects allows to know if the class is shared.

info

• A class inheriting from a non-shared class cannot be defined as shared.
• Shared classes are not supported by ORDA-based classes.

Criação de uma classe compartilhada

To create a shared class, add the shared keyword before the Class Constructor. Por exemplo:

    //shared class: Person
shared Class Constructor($firstname : Text; $lastname : Text)
 This.firstName:=$firstname
 This.lastName:=$lastname

//myMethod
var $person := cs.Person.new("John"; "Smith")
OB Is shared($person) // true
cs.Person.isShared //true

Funções compartilhadas

If a function defined inside a shared class modifies objects of the class, it should call Use...End use structure to protect access to the shared objects. However, to simplify the code, you can define the function as shared so that it automatically triggers internal Use...End use when executed.

To create a shared function, add the shared keyword before the Function keyword in a shared class. Por exemplo:

    //shared class Foo
shared Class Constructor()
  This.variable:=1

shared Function Bar($value : Integer)
  This.variable:=$value //no need to call use/end use

nota

If the shared function keyword is used in a non-shared user class, it is ignored.

Classes Singleton

A singleton class is a user class that only produces a single instance. For more information on singletons, please see the Wikipedia page about singletons.

The class singleton is instantiated at the first call of the cs.<class>.me property. The instantiated class singleton is then always returned when the me property is used.

If you need to instantiate a singleton with parameters, you can also call the new() function. Nesse caso, é recomendado instanciar o singleton em algum código executado no início da aplicação.

O escopo de uma instância singleton pode ser o processo atual ou todos os processos. A process singleton has a unique value for the process in which it is instantiated, while an interprocess singleton has a unique value for all processes of the application. Singletons são úteis para definir valores que precisam estar disponíveis em qualquer lugar em um aplicativo ou processo.

The .isSingleton property of Class objects allows to know if the class is a singleton.

info

Singleton classes are not supported by ORDA-based classes.

Criação de um singleton process

To create a process singleton class, add the singleton keyword before Class Constructor. Por exemplo:

    //class: ProcessTag
singleton Class Constructor()
 This.tag:=Random

Para usar o singleton process:

    //in a process
var $mySingleton := cs.ProcessTag.me //First instantiation
    //$mySingleton.tag = 5425 for example  
...  
var $myOtherSingleton := cs.ProcessTag.me
    //$myOtherSingleton.tag = 5425

    //in another process
var $mySingleton := cs.ProcessTag.me //First instantiation
    //$mySingleton.tag = 14856 for example  
...  
var $myOtherSingleton := cs.ProcessTag.me  
    //$myOtherSingleton.tag = 14856

Criação de um singleton interprocesso

To create an interprocess singleton, add the shared singleton keywords before the Class Constructor. Por exemplo:

//Class VehicleFactory

property vehicleBuilt : Integer

shared singleton Class constructor()
  This.vehicleBuilt := 0 //Number of vehicles built by the factory

shared Function buildVehicle ($type : Text) -> $vehicle : cs.Vehicle

  Case of
    : $type="car"
      $vehicle:=cs.Car.new()
    : $type="truck"
      $vehicle:=cs.Truck.new()
    : $type="sport car"
      $vehicle:=cs.SportCar.new()
    : $type="motorbike"
      $vehicle:=cs.Motorbike.new()
  Else
    $vehicle:=cs.Car.new()
  End case
  This.vehicleBuilt+=1

You can then call the cs.VehicleFactory singleton to get a new vehicle from everywhere in your application with a single line:

$vehicle:=cs.VehicleFactory.me.buildVehicle("caminhão")

Since the buildVehicle() function modifies the cs.VehicleFactory singleton (by incrementing This.vehicleBuilt) you need to add the shared keyword to it.

Veja também

See also this blog post for more details.