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In
class-based Class-based programming, or more commonly class-orientation, is a style of object-oriented programming (OOP) in which inheritance (object-oriented programming), inheritance occurs via defining ''class (computer programming), classes'' of object ...
,
object-oriented programming Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of ...
, a constructor (abbreviation: ctor) is a special type of subroutine called to create an object. It prepares the new object for use, often accepting
arguments An argument is a statement or group of statements called premises intended to determine the degree of truth or acceptability of another statement called conclusion. Arguments can be studied from three main perspectives: the logical, the dialectic ...
that the constructor uses to set required
member variable In object-oriented programming, a member variable (sometimes called a member field) is a variable that is associated with a specific object, and accessible for all its methods (''member functions''). In class-based programming languages, these ...
s. A constructor resembles an
instance method A method in object-oriented programming (OOP) is a procedure associated with a message and an object. An object consists of ''state data'' and ''behavior''; these compose an ''interface'', which specifies how the object may be utilized by any ...
, but it differs from a method in that it has no explicit
return type In computer programming, the return type (or result type) defines and constrains the data type of the value returned from a subroutine or method. In many programming languages (especially statically-typed programming languages such as C, C++, ...
, it is not implicitly inherited and it usually has different rules for scope modifiers. Constructors often have the same name as the declaring
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...
. They have the task of initializing the object's data members and of establishing the invariant of the class, failing if the invariant is invalid. A properly written constructor leaves the resulting
object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an ...
in a ''valid'' state.
Immutable object In object-oriented and functional programming, an immutable object (unchangeable object) is an object whose state cannot be modified after it is created.Goetz et al. ''Java Concurrency in Practice''. Addison Wesley Professional, 2006, Section 3 ...
s must be initialized in a constructor. Most languages allow overloading the constructor in that there can be more than one constructor for a class, with differing parameters. Some languages take consideration of some special types of constructors. Constructors, which concretely use a single class to create objects and return a new instance of the class, are abstracted by
factories A factory, manufacturing plant or a production plant is an industrial facility, often a complex consisting of several buildings filled with machinery, where workers manufacture items or operate machines which process each item into another. T ...
, which also create objects but can do so in various ways, using multiple classes or different allocation schemes such as an
object pool The object pool pattern is a software creational design pattern that uses a set of initialized objects kept ready to use – a "pool" – rather than allocating and destroying them on demand. A client of the pool will request an object from the p ...
.


Types


Parameterized constructors

Constructors that can take at least one argument are termed as parameterized constructors. When an object is declared in a parameterized constructor, the initial values have to be passed as arguments to the constructor function. The normal way of object declaration may not work. The constructors can be called explicitly or implicitly. The method of calling the constructor implicitly is also called the shorthand method. class Example ; Example::Example() = default; Example::Example(int x, int y) : x_(x), y_(y) Example e = Example(0, 50); // Explicit call. Example e2(0, 50); // Implicit call.


Default constructors

If the programmer does not supply a constructor for an instantiable class, Java compiler inserts a
default constructor In computer programming languages, the term default constructor can refer to a constructor that is automatically generated by the compiler in the absence of any programmer-defined constructors (e.g. in Java), and is usually a nullary constructor. I ...
into your code on your behalf. This constructor is known as default constructor. You would not find it in your source code (the java file) as it would be inserted into the code during compilation and exists in .class file. The behavior of the default constructor is language dependent. It may initialize data members to zero or other same values, or it may do nothing at all. In Java, a "default constructor" refer to a nullary constructor that is automatically generated by the compiler if no constructors have been defined for the class or in the absence of any programmer-defined constructors (e.g. in Java, the default constructor implicitly calls the superclass's nullary constructor, then executes an empty body). All fields are left at their initial value of 0 (integer types), 0.0 (floating-point types), false (boolean type), or null (reference types). #include class Student ;


Copy constructors

Like C++, Java also supports "Copy Constructor". But, unlike C++, Java doesn't create a default copy constructor if you don't write your own. Copy constructors define the actions performed by the compiler when copying class objects. A Copy constructor has one formal parameter that is the type of the class (the parameter may be a reference to an object). It is used to create a copy of an existing object of the same class. Even though both classes are the same, it counts as a conversion constructor. While copy constructors are usually abbreviated copy ctor or cctor, they have nothing to do with class constructors used in .NET using the same abbreviation.


Conversion constructors

Conversion constructors provide a means for a compiler to implicitly create an object belonging to one class based on an object of a different type. These constructors are usually invoked implicitly to convert arguments or operands to an appropriate type, but they may also be called explicitly.


Move constructors

In C++, move constructors take an Rvalue reference to an object of the class, and are used to implement ownership transfer of the parameter object's resources.


Syntax

*
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...
,
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
, C#,
ActionScript ActionScript is an object-oriented programming language originally developed by Macromedia Inc. (later acquired by Adobe). It is influenced by HyperTalk, the scripting language for HyperCard. It is now an implementation of ECMAScript (meaning ...
, and
MATLAB MATLAB (an abbreviation of "MATrix LABoratory") is a proprietary multi-paradigm programming language and numeric computing environment developed by MathWorks. MATLAB allows matrix manipulations, plotting of functions and data, implementa ...
have a naming convention in which constructors have the same name as the class with which they are associated. * In PHP 5, a recommended name for a constructor is __construct. For backwards compatibility, a method with the same name as the class will be called if __construct method can not be found. Since PHP 5.3.3, this works only for non-namespaced classes.Constructors and Destructors
from PHP online documentation
* In PHP 7, you should always name the constructor as __construct. Methods with the same name as the class will trigger an E_DEPRECATED level error.Constructors and Destructors
from PHP online documentation
* In
Perl Perl is a family of two high-level, general-purpose, interpreted, dynamic programming languages. "Perl" refers to Perl 5, but from 2000 to 2019 it also referred to its redesigned "sister language", Perl 6, before the latter's name was offic ...
, constructors are, by convention, named "new" and have to do a fair amount of object creation. * In Moose object system for Perl, constructors (named ''new'') are automatically created and are extended by specifying a ''BUILD'' method. * In
Visual Basic .NET Visual Basic, originally called Visual Basic .NET (VB.NET), is a multi-paradigm, object-oriented programming language, implemented on .NET, Mono, and the .NET Framework. Microsoft launched VB.NET in 2002 as the successor to its original Visua ...
, the constructor is called "New". * In
Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...
, the constructor is split over two methods, "__new__" and "__init__". The __new__ method is responsible for allocating memory for the instance, and receives the class as an argument (conventionally called "cls"). The __init__ method (often called "the initialiser") is passed the newly created instance as an argument (conventionally called "self"). *
Object Pascal Object Pascal is an extension to the programming language Pascal (programming language), Pascal that provides object-oriented programming (OOP) features such as Class (computer programming), classes and Method (computer programming), methods. ...
constructors are signified by the keyword "constructor" and can have user-defined names (but are mostly called "Create"). * In
Objective-C Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. Originally developed by Brad Cox and Tom Love in the early 1980s, it was selected by NeXT for its NeXTS ...
, the constructor method is split across two methods, "alloc" and "init" with the alloc method setting aside (allocating) memory for an instance of the class, and the init method handling the bulk of initializing the instance. A call to the method "new" invokes both the alloc and the init methods, for the class instance.


Memory organization

In Java, C#, and VB .NET, the constructor creates reference type objects in a special memory structure called the " heap". Value types (such as int, double, etc.) are created in a sequential structure called the " stack". VB .NET and C# also allow the use of the ''new'' operator to create value type objects, but these value type objects are created on the stack regardless of whether the operator is used or not. In C++, objects are created on the stack when the constructor is invoked without the new operator, and created on the heap when the constructor is invoked with the new operator. Stack objects are deleted implicitly when they go out of scope, while heap objects must be deleted implicitly by a destructor or explicitly by using the ''delete'' operator.


Language details


C++

In
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
, the name of the constructor is the name of the class. It returns nothing. It can have parameters like any
member function A method in object-oriented programming (OOP) is a procedure associated with a message and an object. An object consists of ''state data'' and ''behavior''; these compose an ''interface'', which specifies how the object may be utilized by any of ...
. Constructor functions are usually declared in the public section, but can also be declared in the protected and private sections, if the user wants to restrict access to them. The constructor has two parts. First is the
initializer list In computer programming, initialization (or initialisation) is the assignment of an initial value for a data object or variable. The manner in which initialization is performed depends on the programming language, as well as the type, storage class ...
which follows the parameter list and before the method body. It starts with a colon and entries are comma-separated. The initializer list is not required, but offers the opportunity to provide values for data members and avoid separate assignment statements. The initializer list is required if you have ''const'' or reference type data members, or members that do not have parameterless constructor logic. Assignments occur according to the order in which data members are declared (even if the order in the initializer list is different). The second part is the body, which is a normal method body enclosed in curly brackets. C++ allows more than one constructor. The other constructors must have different parameters. Additionally constructors which contain parameters which are given default values, must adhere to the restriction that not all parameters are given a default value. This is a situation which only matters if there is a default constructor. The constructor of a
base class In object-oriented programming, inheritance is the mechanism of basing an object or class upon another object ( prototype-based inheritance) or class ( class-based inheritance), retaining similar implementation. Also defined as deriving new classe ...
(or base classes) can also be called by a derived class. Constructor functions are not inherited and their addresses cannot be referenced. When memory allocation is required, the ''new'' and ''delete'' operators are called implicitly. A copy constructor has a parameter of the same type passed as ''const'' reference, for example ''Vector(const Vector& rhs)''. If it is not provided explicitly, the compiler uses the copy constructor for each member variable or simply copies values in case of primitive types. The default implementation is not efficient if the class has dynamically allocated members (or handles to other resources), because it can lead to double calls to ''delete'' (or double release of resources) upon destruction. class Foobar ; Example invocations: Foobar a, b(3), c(5, M_PI/4); On returning objects from functions or passing objects by value, the objects copy constructor will be called implicitly, unless
return value optimization In C++ computer programming, copy elision refers to a compiler optimization technique that eliminates unnecessary copying of objects. The C++ language standard generally allows implementations to perform any optimization, provided the resulting pr ...
applies. C++ implicitly generates a default copy constructor which will call the copy constructors for all base classes and all member variables unless the programmer provides one, explicitly deletes the copy constructor (to prevent cloning) or one of the base classes or member variables copy constructor is deleted or not accessible (private). Most cases calling for a customized copy constructor (e.g. reference counting, deep copy of pointers) also require customizing the destructor and the copy assignment operator. This is commonly referred to as the Rule of three.


C#

Example C# constructor: public class MyClass // Code somewhere // Instantiating an object with the constructor above MyClass c = new MyClass(42, "string");


C# static constructor

In C#, a ''static constructor'' is a static data initializer. Static constructors are also called ''class constructors''. Since the actual method generated has the name ''.cctor'' they are often also called "cctors". Static constructors allow complex static variable initialization. Static constructors are called implicitly when the class is first accessed. Any call to a class (static or constructor call), triggers the static constructor execution. Static constructors are
thread safe Thread safety is a computer programming concept applicable to multi-threaded code. Thread-safe code only manipulates shared data structures in a manner that ensures that all threads behave properly and fulfill their design specifications without uni ...
and implement a
singleton pattern In software engineering, the singleton pattern is a software design pattern that restricts the instantiation of a class to a singular instance. One of the well-known "Gang of Four" design patterns, which describe how to solve recurring problems ...
. When used in a
generic programming Generic programming is a style of computer programming in which algorithms are written in terms of types ''to-be-specified-later'' that are then ''instantiated'' when needed for specific types provided as parameters. This approach, pioneered b ...
class, static constructors are called at every new generic instantiation one per type. Static variables are instantiated as well. public class MyClass // Code somewhere // Instantiating an object with the constructor above // right before the instantiation // The variable static constructor is executed and _A is 32 MyClass c = new MyClass();


CFML

CFML ColdFusion Markup Language, more commonly known as CFML, is a scripting language for web development that runs on the JVM, the .NET framework, and Google App Engine. Multiple commercial and open source implementations of CFML engines are availab ...
uses a method named 'init' as a constructor method. Cheese.cfc component Create instance of a cheese. myCheese = new Cheese( 'Cheddar' ); Since ColdFusion 10, CFML has also supported specifying the name of the constructor method: component initmethod="Cheese"


Eiffel

In
Eiffel Eiffel may refer to: Places * Eiffel Peak, a summit in Alberta, Canada * Champ de Mars – Tour Eiffel station, Paris, France; a transit station Structures * Eiffel Tower, in Paris, France, designed by Gustave Eiffel * Eiffel Bridge, Ungheni, M ...
, the routines which initialize new objects are called ''creation procedures''. Creation procedures have the following traits: * Creation procedures have no explicit return type (by definition of ''procedure''). * Creation procedures are named. * Creation procedures are designated by name as creation procedures in the text of the class. * Creation procedures can be explicitly invoked to re-initialize existing objects. * Every effective (i.e., concrete or non-abstract) class must designate at least one creation procedure. * Creation procedures must leave the newly initialized object in a state that satisfies the class invariant. Although object creation involves some subtleties,Eiffel ISO/ECMA specification document
/ref> the creation of an attribute with a typical declaration x: T as expressed in a creation instruction create x.make consists of the following sequence of steps: * Create a new direct instance of type T. * Execute the creation procedure make to the newly created instance. * Attach the newly initialized object to the entity x. In the first snippet below, class POINT is defined. The procedure make is coded after the keyword feature. The keyword create introduces a list of procedures which can be used to initialize instances. In this case the list includes default_create, a procedure with an empty implementation inherited from class ANY, and the make procedure coded within the class. class POINT create default_create, make feature make (a_x_value: REAL; a_y_value: REAL) do x := a_x_value y := a_y_value end x: REAL -- X coordinate y: REAL -- Y coordinate ... In the second snippet, a class which is a client to POINT has a declarations my_point_1 and my_point_2 of type POINT. In procedural code, my_point_1 is created as the origin (0.0, 0.0). Because no creation procedure is specified, the procedure default_create inherited from class ANY is used. This line could have been coded create my_point_1.default_create . Only procedures named as creation procedures can be used in an instruction with the create keyword. Next is a creation instruction for my_point_2, providing initial values for the my_point_2's coordinates. The third instruction makes an ordinary instance call to the make procedure to reinitialize the instance attached to my_point_2 with different values. my_point_1: POINT my_point_2: POINT ... create my_point_1 create my_point_2.make (3.0, 4.0) my_point_2.make (5.0, 8.0) ...


F#

In F#, a constructor can include any let or do statements defined in a class. let statements define private fields and do statements execute code. Additional constructors can be defined using the new keyword. type MyClass(_a : int, _b : string) = class // Primary constructor let a = _a let b = _b do printfn "a = %i, b = %s" a b // Additional constructors new(_a : int) = MyClass(_a, "") then printfn "Integer parameter given" new(_b : string) = MyClass(0, _b) then printfn "String parameter given" new() = MyClass(0, "") then printfn "No parameter given" end // Code somewhere // instantiating an object with the primary constructor let c1 = new MyClass(42, "string") // instantiating an object with additional constructors let c2 = new MyClass(42) let c3 = new MyClass("string") let c4 = MyClass() // "new" keyword is optional


Java

In
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's mos ...
, constructors differ from other methods in that: * Constructors never have an explicit return type. * Constructors cannot be directly invoked (the keyword “new” invokes them). * Constructors should not have non-access modifiers. Java constructors perform the following tasks in the following order: # Call the default constructor of the superclass if no constructor is defined. # Initialize member variables to the specified values. # Executes the body of the constructor. Java permit users to call one constructor in another constructor using this() keyword. But this() must be first statement. class Example public static void main(String[] args) Java provides access to the superclass (computer science), superclass's constructor through the super keyword. public class Example // Code somewhere else // Instantiating an object with the above constructor Example e = new Example(42); A constructor taking zero number of arguments is called a "no-arguments" or "no-arg" constructor.


JavaScript

As of ES6,
JavaScript JavaScript (), often abbreviated as JS, is a programming language that is one of the core technologies of the World Wide Web, alongside HTML and CSS. As of 2022, 98% of Website, websites use JavaScript on the Client (computing), client side ...
has direct constructors like many other programming languages. They are written as such class FooBar This can be instantiated as such const foo = new FooBar('7') The equivalent of this before ES6, was creating a function that instantiates an object as such function FooBar (baz) This is instantiated the same way as above.


Object Pascal

In
Object Pascal Object Pascal is an extension to the programming language Pascal (programming language), Pascal that provides object-oriented programming (OOP) features such as Class (computer programming), classes and Method (computer programming), methods. ...
, the constructor is similar to a
factory method In class-based programming, the factory method pattern is a creational pattern that uses factory methods to deal with the problem of creating objects without having to specify the exact class of the object that will be created. This is done by cr ...
. The only syntactic difference to regular methods is the keyword constructor in front of the name (instead of procedure or function). It can have any name, though the convention is to have Create as prefix, such as in CreateWithFormatting. Creating an instance of a class works like calling a static method of a class: TPerson.Create('Peter'). program OopProgram; type TPerson = class private FName: string; public property Name: string read FName; constructor Create(AName: string); end; constructor TPerson.Create(AName: string); begin FName := AName; end; var Person: TPerson; begin Person := TPerson.Create('Peter'); // allocates an instance of TPerson and then calls TPerson.Create with the parameter AName = 'Peter' end.


OCaml

In
OCaml OCaml ( , formerly Objective Caml) is a general-purpose programming language, general-purpose, multi-paradigm programming language which extends the Caml dialect of ML (programming language), ML with object-oriented programming, object-oriented ...
, there is one constructor. Parameters are defined right after the class name. They can be used to initialize instance variables and are accessible throughout the class. An anonymous hidden method called initializer allows to evaluate an expression immediately after the object has been built. class person first_name last_name = object val full_name = first_name ^ " " ^ last_name initializer print_endline("Hello there, I am " ^ full_name ^ ".") method get_last_name = last_name end;; let alonzo = new person "Alonzo" "Church" in (*Hello there, I am Alonzo Church.*) print_endline alonzo#get_last_name (*Church*)


PHP

In
PHP PHP is a general-purpose scripting language geared toward web development. It was originally created by Danish-Canadian programmer Rasmus Lerdorf in 1993 and released in 1995. The PHP reference implementation is now produced by The PHP Group. ...
version 5 and above, the constructor is a method named __construct() (notice that it's a double underscore), which the keyword new automatically calls after creating the object. It is usually used to automatically perform initializations such as property initializations. Constructors can also accept arguments, in which case, when the new statement is written, you also need to send the constructor arguments for the parameters. class Person In PHP, a class is only allowed to declare a maximum of one constructor method. Static methods, factory classes or optional constructor arguments are some ways to facilitate multiple ways to create objects of a PHP class.


Perl 5

In Perl programming language version 5, by default, constructors are
factory method In class-based programming, the factory method pattern is a creational pattern that uses factory methods to deal with the problem of creating objects without having to specify the exact class of the object that will be created. This is done by cr ...
s, that is, methods that create and return the object, concretely meaning create and return a blessed reference. A typical object is a reference to a hash, though rarely references to other types are used too. By convention the only constructor is named ''new'', though it is allowed to name it otherwise, or to have multiple constructors. For example, a Person class may have a constructor named ''new'' as well as a constructor ''new_from_file'' which reads a file for Person attributes, and ''new_from_person'' which uses another Person object as a template. package Person; # In Perl constructors are named 'new' by convention. sub new 1;


Perl 5 with Moose

With the Moose object system for Perl, most of this boilerplate can be left out, a default ''new'' is created, attributes can be specified, as well as whether they can be set, reset, or are required. In addition, any extra constructor functionality can be included in a ''BUILD'' method which the Moose generated constructor will call, after it has checked the arguments. A ''BUILDARGS'' method can be specified to handle constructor arguments not in hashref / key => value form. package Person; # enable Moose-style object construction use Moose; # first name ( a string) can only be set at construction time ('ro') has first_name => (is => 'ro', isa => 'Str', required => 1); # last name ( a string) can only be set at construction time ('ro') has last_name => (is => 'ro', isa => 'Str', required => 1); # age (Integer) can be modified after construction ('rw'), and is not required # to be passed to be constructor. Also creates a 'has_age' method which returns # true if age has been set has age => (is => 'rw', isa => 'Int', predicate => 'has_age'); # Check custom requirements sub BUILD 1; In both cases the Person class is instiated like this: use Person; my $p = Person->new( first_name => 'Sam', last_name => 'Ashe', age => 42 );


Python

In
Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (pro ...
, constructors are defined by one or both of __new__ and __init__ methods. A new instance is created by calling the class as if it were a function, which calls the __new__ and __init__ methods. If a constructor method is not defined in the class, the next one found in the class's Method Resolution Order will be called. In the typical case, only the __init__ method need be defined. (The most common exception is for immutable objects.) >>> class ExampleClass: ... def __new__(cls, value): ... print("Creating new instance...") ... # Call the superclass constructor to create the instance. ... instance = super(ExampleClass, cls).__new__(cls) ... return instance ... def __init__(self, value): ... print("Initialising instance...") ... self.payload = value >>> exampleInstance = ExampleClass(42) Creating new instance... Initialising instance... >>> print(exampleInstance.payload) 42 Classes normally act as
factories A factory, manufacturing plant or a production plant is an industrial facility, often a complex consisting of several buildings filled with machinery, where workers manufacture items or operate machines which process each item into another. T ...
for new instances of themselves, that is, a class is a callable object (like a function), with the call being the constructor, and calling the class returns an instance of that class. However the __new__ method is permitted to return something other than an instance of the class for specialised purposes. In that case, the __init__ is not invoked.Data model
/ref>


Raku

With Raku, even more boilerplate can be left out, given that a default ''new'' method is inherited, attributes can be specified, as well as whether they can be set, reset, or are required. In addition, any extra constructor functionality can be included in a ''BUILD'' method which will get called to allow for custom initialization. A ''TWEAK'' method can be specified to post-process any attributes already (implicitly) initialized. class Person The Person class is instantiated like this: my $p0 = Person.new( first-name => 'Sam', last-name => 'Ashe', age => 42 ); my $p1 = Person.new( first-name => 'grace', last-name => 'hopper' ); say $p1.full-name(); # OUTPUT: «Grace Hopper␤» Alternatively, the
named parameter In computer programming, named parameters, named argument or keyword arguments refer to a computer language's support for function calls that clearly state the name of each parameter within the function call. Overview A function call using na ...
s can be specified using the colon-pair syntax in Perl 6: my $p0 = Person.new( :first-name, :last-name, :age(42) ); my $p1 = Person.new( :first-name, :last-name ); And should you have set up variables with names identical to the named parameters, you can use a shortcut that will use the name of the variable for the named parameter: my $first-name = "Sam"; my $last-name = "Ashe"; my $age = 42; my $p0 = Person.new( :$first-name, :$last-name, :$age );


Ruby

In
Ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sa ...
, constructors are created by defining a method called initialize. This method is executed to initialize each new instance. irb(main):001:0> class ExampleClass irb(main):002:1> def initialize irb(main):003:2> puts "Hello there" irb(main):004:2> end irb(main):005:1> end => nil irb(main):006:0> ExampleClass.new Hello there => #


Visual Basic .NET

In
Visual Basic .NET Visual Basic, originally called Visual Basic .NET (VB.NET), is a multi-paradigm, object-oriented programming language, implemented on .NET, Mono, and the .NET Framework. Microsoft launched VB.NET in 2002 as the successor to its original Visua ...
, constructors use a method declaration with the name "New". Class Foobar Private strData As String ' Constructor Public Sub New(ByVal someParam As String) strData = someParam End Sub End Class ' code somewhere else ' instantiating an object with the above constructor Dim foo As New Foobar(".NET")


See also

* RAII * Allocation site *
Creational pattern In software engineering, creational design patterns are design patterns that deal with object creation mechanisms, trying to create objects in a manner suitable to the situation. The basic form of object creation could result in design problems or ...
* Destructor * Global constructor in C++, and its C counterpart,
((constructor)) (also known as ) is a set of execution startup routines Linker (computing), linked into a C (programming language), C program that performs any initialization work required before calling the program's main function. Form and usage Crt0 gener ...
function attribute


Notes


References

{{Reflist, 30em Method (computer programming) Programming language comparisons