Virtual class methods and properties

[pyscripter 719]

The following will not compile (error: class property accessor can be a class field or a static class method) :

 

  TTest = class
  private
    class function GetName: string; virtual; abstract;
  public
    class property Name: string read GetName;
  end;

 

whilst the following does:

 

  TTest = class
  private
    class function GetName: string; virtual; abstract;
  public
    property Name: string read GetName;
  end;

 

My question is that since you can have virtual class methods, why not properties that behave accordingly? 

 

In SmallTalk, the first object oriented language, you have a distinction between:

• instance variables (aka properties)
• class variables (aka class properties - one per class including subclasses)
• class instance variables  (one per class, subclasses can change the value)

[Vincent Parrett 807]

Class property Getter/Setters must be static, however delphi doesn't allow virtual abstract static methods. I don't see a good reason for this, so it's likely technical or an oversight. 

 

[Uwe Raabe 2094]

46 minutes ago, Vincent Parrett said:

I don't see a good reason for this

Static class methods miss the implicit Self parameter, which holds the current type called. They are quite similar to global procedures/functions and therefore they cannot be virtual - there is just no VMT available. It is the same reason why static class methods cannot call virtual methods.

[pyscripter 719]

@Uwe Raabe Sure but why can't you have a class property that has virtual class method accessor.  It is just "syntactic sugar".  You call the virtual class method to get the value.

Edited 7 hours ago by pyscripter