“严格私人”和“受保护”访问修饰符在Delphi？ [英] Difference between "strict private" and "protected" Access Modifiers in Delphi?

问题描述

但是我用Pascal语言学习编程和结构化编程之后，我开始用Delphi了解OOP。

but I learn programming and after structured programming with Pascal language, I'm beginning to learn about OOP with Delphi.

所以，我真的不明白 strict private 指令和受保护的一个..所以这里是我的代码，它是关于一个包创建时，只是介绍了我的Delphi的课程，老师向我们展示了如何创建对象：

So, I don't really understand the difference between the strict private instruction and the protected one.. So here is my code, it's about a "bag" creation, it's just the introduction of my Delphi's lesson, teacher show us how we can create objects:

    uses
  SysUtils;

Type

  Tbag= class (Tobject)                                                          
    strict private                                                                
      FcontenM : single;
      Fcontent : single;
    protected
      function getisempty : boolean;
      function getisfull: boolean;
    public
      constructor creer (nbliters : single);
      procedure add     (nbliters : single);
      procedure clear   (nbliters : single);
      property contenM : single read FcontenM;
      property content : single read Fcontent;
      property isempty : boolean read getisempty;
      property isfull : boolean read getisfull;
    end;


function Tseau.getisempty;
  begin
    result := Fcontent = 0;
  end;

function Tseau.getisfull;
  begin
    result := Fcontent = FcontenM;
  end;

constructor Tseau.creer(nbliters: Single);
  begin
    inherited create;
    FcontenM := nbliters;
  end;

procedure Tbag.add (nbliters: Single);
  begin
    if ((FcontenM - Fcontent) < nbliters) then fcontent := fcontenM
      else Fcontent := (Fcontent + nbliters);
  end;

procedure Tbag.clear (nbliters: Single);
  begin
    if (Fcontent > nbliters) then Fcontent := (Fcontent - nbliters)
      else Fcontent := 0;
  end;

所以这只是对象创建的一个例子;我明白什么是公共声明（外界可接受的界面），但是我看不到私有和受保护的声明有什么区别..感谢您试图帮助我..

So it's just an example of object creation; I understand what is public declaration (interface approachable by the outside) but I don't see what's the difference between private and protected declarations.. Thanks for trying to help me..

推荐答案

私人，受保护和公开之间的区别非常简单：

The difference between private, protected and public is pretty straightforward:

• 私人会员/方法只有在声明它们的类中才可见。


• 受保护的成员/方法在类中可见，和到所有子类。


• 所有其他类都可以看到公共成员和方法。

• Private members/methods are only visible within the class that declares them.
• Protected members/methods are visible within the class, and to all subclasses.
• Public members and methods are visible to all other classes.

在Delphi中有一个错误，使所有成员在同一个单位内公开的可见性。 严格关键字可以纠正此问题，因此即使在单个单元中，私有功能也是私有的。对于良好的封装，我建议始终使用strict关键字。

In Delphi there's a "bug" that makes the visibility of all members public within the same unit. The strict keyword corrects this behaviour, so that private is actually private, even within a single unit. For good encapsulation I would recommend always using the strict keyword.

示例代码：

type
  TFather = class
  private
    FPriv : integer;
  strict private
    FStrPriv : integer;
  protected
    FProt : integer;
  strict protected
    FStrProt : integer;
  public
    FPublic : integer;
  end;

  TSon = class(TFather)
  public
    procedure DoStuff;
  end;

  TUnrelated = class
  public
    procedure DoStuff;
  end;

procedure TSon.DoStuff;
begin
  FProt := 10;       // Legal, as it should be. Accessible to descendants.
  FPriv := 100;      // Legal, even though private. This won't work from another unit!
  FStrictPriv := 10; // <- Compiler Error, FStrictPrivFather is private to TFather
  FPublic := 100;    // Legal, naturally. Public members are accessible from everywhere.
end;

procedure TUnrelated.DoStuff;
var
  F : TFather;
begin
  F := TFather.Create;
  try
    F.FProt := 10;     // Legal, but it shouldn't be!
    F.FStrProt := 100; // <- Compiler error, the strict keyword has "made the protection work"
    F.FPublic := 100;  // Legal, naturally.
  finally
    F.Free;
  end;
end;

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