프로퍼티 (프로그래밍)

프로퍼티(property)는 일부 객체 지향 프로그래밍 언어에서 필드(데이터 멤버)와 메소드 간 기능의 중간인 클래스 멤버의 특수한 유형이다. 프로퍼티의 읽기와 쓰기는 일반적으로 게터(getter)와 세터(setter) 메소드 호출로 변환된다.

 지원 언어 
프로퍼티를 지원하는 프로그래밍 언어에는 액션스크립트 3, C#, D, 델파이/프리 파스칼, eC, 코틀린, 자바스크립트, 오브젝티브-C 2.0, 파이썬, 스칼라, 스위프트, 루아, 비주얼 베이직이 있다.

자바, C++과 같은 일부 객체 지향 언어들은 프로퍼티를 지원하지 않기 때문에 프로그래머가 한 쌍의 액세서(accessor)와 뮤테이터(mutator) 메소드를 대신 정의해야 한다.

 문법 예시 
 C# 
class Pen
{
 private int color; // private field

 // public property
 public int Color
 {
 get
 {
 return this.color;
 }
 set
 {
 if (value > 0) {
 this.color = value;
 }
 }
 }
}

// accessing:
Pen pen = new Pen();
int color_tmp = 0;
// ...
pen.Color = 17;
color_tmp = pen.Color;
// ...
pen.Color = ~pen.Color; // bitwise complement ...

// another silly example:
pen.Color += 1; // a lot clearer than "pen.set_Color(pen.get_Color() + 1)"!

class Shape
{

 public Int32 Height { get; set; }
 public Int32 Width { get; private set; }

}

 C++ 
#include 

template 
 class property {
 T value;
 public:
 T & operator = (const T &i) {
 return value = i;
 }
 // This template class member function template serves the purpose to make
 // typing more strict. Assignment to this is only possible with exact identical
 // types.
 template 
 T2 & operator = (const T2 &i) {
 T2 &guard = value;
 throw guard; // Never reached.
 }

 // Implicit conversion back to T.
 operator T const & () const {
 return value;
 }
};

struct Foo {
 // Properties using unnamed classes.
 class {
 int value;
 public:
 int & operator = (const int &i) { return value = i; }
 operator int () const { return value; }
 } alpha;

 class {
 float value;
 public:
 float & operator = (const float &f) { return value = f; }
 operator float () const { return value; }
 } bravo;
};

struct Bar {
 // Using the property<>-template.
 property 
 alpha;
 property 
 bravo;
};

int main () {
 Foo foo;
 foo.alpha = 5;
 foo.bravo = 5.132f;

 Bar bar;
 bar.alpha = true;
 bar.bravo = true; // This line will yield a compile time error
 // due to the guard template member function.
 ::std::cout << foo.alpha << ", "
 << foo.bravo << ", "
 << bar.alpha << ", "
 << bar.bravo
 << ::std::endl;
 return 0;
}

 C++, Microsoft & C++Builder-specific 

예시 출처: MSDN 설명 문서

// declspec_property.cpp
struct S
{
 int i;
 void putprop(int j)
 {
 i = j;
 }

 int getprop()
 {
 return i;
 }

 __declspec(property(get = getprop, put = putprop)) int the_prop;
};

int main()
{
 S s;
 s.the_prop = 5;
 return s.the_prop;
}

 D 

class Pen
{
 private int m_color; // private field

 // public get property
 public int color () {
 return m_color;
 }

 // public set property
 public void color (int value) {
 m_color = value;
 }
}

auto pen = new Pen;
pen.color = ~pen.color; // bitwise complement

// the set property can also be used in expressions, just like regular assignment
int theColor = (pen.color = 0xFF0000);

In D version 2, each property accessor or mutator must be marked with @property:

class Pen
{
 private int m_color; // private field

 // public get property
 @property public int color () {
 return m_color;
 }

 // public set property
 @property public void color (int value) {
 m_color = value;
 }
}

 Delphi/Free Pascal 
type TPen = class
 private
 FColor: TColor;
 function GetColor: TColor;
 procedure SetColor(const AValue: TColor);
 public
 property Color: Integer read GetColor write SetColor;
end;

function TPen.GetColor: TColor;
begin
 Result := FColor;
end;

procedure TPen.SetColor(const AValue: TColor);
begin
 if FColor <> AValue
 then FColor := AValue;
end;

// accessing:
var Pen: TPen;
// ...
Pen.Color := not Pen.Color;

(*
Delphi also supports a 'direct field' syntax -

property Color: TColor read FColor write SetColor;

or

property Color: TColor read GetColor write FColor;

where the compiler generates the exact same code as for reading and writing
a field. This offers the efficiency of a field, with the safety of a property.
(You can't get a pointer to the property, and you can always replace the member
access with a method call.)
*)

 eC 
class Pen
{
 // private data member
 Color color;
public:
 // public property
 property Color color
 {
 get { return color; }
 set { color = value; }
 }
}
Pen blackPen { color = black };
Pen whitePen { color = white };
Pen pen3 { color = { 30, 80, 120 } };
Pen pen4 { color = ColorHSV { 90, 20, 40 } };
 F# 
type Pen() = class
 let mutable _color = 0

 member this.Color
 with get() = _color
 and set value = _color <- value
end

 JavaScript 
function Pen() {
 this._color = 0;
}
// Add the property to the Pen type itself, can also
// be set on the instance individually
Object.defineProperties(Pen.prototype, {
 color: {
 get: function () {
 return this._color;
 },
 set: function (value) {
 this._color = value;
 }
 }
});
var pen = new Pen();
pen.color = ~pen.color; // bitwise complement
pen.color += 1; // Add one

 ActionScript 3.0 
package {
 public class Pen {
 private var _color:uint = 0;

 public function get color():uint {
 return _color;
 }

 public function set color(value:uint):void {
 _color = value;
 }
 }
}
var pen:Pen = new Pen();
pen.color = ~pen.color; // bitwise complement
pen.color += 1; // add one

 Objective-C 2.0 
@interface Pen : NSObject
@property (copy) NSColor *colour; // The "copy" attribute causes the object's copy to be
 // retained, instead of the original.
@end

@implementation Pen
@synthesize colour; // Compiler directive to synthesise accessor methods.
 // It can be left behind in Xcode 4.5 and later.
@end

위 예제는 다음과 같이 임의의 메소드 안에 사용이 가능하다:

Pen *pen = [[Pen alloc] init];
pen.colour = [NSColor blackColor];
float red = pen.colour.redComponent;
[pen.colour drawSwatchInRect: NSMakeRect(0, 0, 100, 100)];

 PHP 
class Pen
{
 private int $color = 1;

 function __set($property, $value)
 {
 if (property_exists($this, $property)) {
 $this->$property = $value;
 }
 }

 function __get($property)
 {
 if (property_exists($this, $property)) {
 return $this->$property;
 }
 return null;
 }
}

$p = new Pen();
$p->color = ~$p->color; // Bitwise complement
echo $p->color;

 Python 
class Pen(object):
 def __init__(self) -> None:
 self._color = 0 # "private" variable

 @property
 def color(self):
 return self._color

 @color.setter
 def color(self, color):
 self._color = color

pen = Pen()
# Accessing:
pen.color = ~pen.color # Bitwise complement ...

 Ruby 
class Pen
 def initialize
 @color = 0
 end

 # Defines a getter for the @color field
 def color
 @color
 end

 # Defines a setter for the @color field
 def color=(value)
 @color = value
 end
end

pen = Pen.new
pen.color = ~pen.color # Bitwise complement

루비는 또한 클래스의 인스턴스 메소드로 정의되는 자동 게터/세터 신시사이저를 제공한다.

class Pen
 attr_reader :brand # Generates a getter for @brand (Read-Only)
 attr_writer :size # Generates a setter for @size (Write-Only)
 attr_accessor :color # Generates both a getter and setter for @color (Read/Write)

 def initialize
 @color = 0 # Within the object, we can access the instance variable directly
 @brand = "Penbrand"
 @size = 0.7 # But we could also use the setter method defined by the attr_accessor Class instance method
 end
end

pen = Pen.new
puts pen.brand # Accesses the pen brand through the generated getter
pen.size = 0.5 # Updates the size field of the pen through the generated setter
pen.color = ~pen.color

 Visual Basic 

 Visual Basic (.NET 2003-2010) 
Public Class Pen

 Private _color As Integer ' Private field

 Public Property Color() As Integer ' Public property
 Get
 Return _color
 End Get
 Set(ByVal value As Integer)
 _color = value
 End Set
 End Property

End Class

' Create Pen class instance
Dim pen As New Pen()

' Set value
pen.Color = 1

' Get value
Dim color As Int32 = pen.Color

 Visual Basic (only .NET 2010) 
Public Class Pen

 Public Property Color() As Integer ' Public property

End Class

' Create Pen class instance
Dim pen As New Pen()

' Set value
pen.Color = 1

' Get value
Dim color As Int32 = pen.Color

 Visual Basic 6 
' in a class named clsPen
Private m_Color As Long

Public Property Get Color() As Long
 Color = m_Color
End Property

Public Property Let Color(ByVal RHS As Long)
 m_Color = RHS
End Property

' accessing:
Dim pen As New clsPen
' ...
pen.Color = Not pen.Color

 같이 보기 
 속성 (컴퓨터 과학)
 데이터 바인딩
 인덱서 (프로그래밍)
 메서드 (컴퓨터 프로그래밍)
 뮤테이터 메소드

분류:객체 지향 프로그래밍