[fpc-devel] Compile time functions

[Thorsten Engler]

type

  TMyClass = class of TMyObject;

  TMyObject = class

    procedure InstanceMethod; //Self = TMyObject, can be virtual

    class procedure ClassMethod; //Self = TMyClass, can be virtual

    class procedure StaticClassMethod; static; //no Self, really just a global procedure in a scoped namespace

  end;

 

var

  o: TMyObject;

  c: TMyClass;

begin

  o.InstanceMethod; //if virtual, calls resolved based on actual class

  o.ClassMethod; //if virtual calls, resolved based on actual class

  o.StaticCalssMethod; //can’t be virtual, resolved on variable type

 

  TMyObject.ClassMethod; //call resolved based on given type

  TMyObject.StaticClassMethod; //call resolved based on given type

 

  c.ClassMethod; //if virtual, calls resolved based on actual class

  //haven’t tried if this one works, I assume it does:

  c.StaticClassMethod; //can’t be virtual, resolved on variable type

end;

 

From: fpc-devel <fpc-devel-bounces at lists.freepascal.org> On Behalf Of J. Gareth Moreton
Sent: Sunday, 29 July 2018 07:22
To: FPC developers' list <fpc-devel at lists.freepascal.org>
Subject: Re: [fpc-devel] Compile time functions

 

Aah, right.  Class methods I have used in past projects, but my understanding is that, in these instances, Self can still be accessed, but represents the class rather than the object, can be called without an instantiated object, and still have the issues that they can be virtual and overridden (something i'm disallowing with pure functions because of the initial complexity of determining which version of a method to call).

Can you clarify, Sven, with "static" and "class"?

 

Gareth aka. Kit


On Sat 28/07/18 23:11 , "Dmitry Boyarintsev" skalogryz.lists at gmail.com <mailto:skalogryz.lists at gmail.com>  sent:

These are known as “class” methods (rather than “static”) in object pascal.

 

Thanks,

Dmitry

On Saturday, July 28, 2018, J. Gareth Moreton <gareth at moreton-family.com <javascript:top.opencompose('gareth at moreton-family.com','','','')> > wrote:

Aah, right.

 

I'm probably being rather dumb here from not having used them before, but do you mean things like this?

type
  TNewClass = class

    function Special: Boolean; static;

end;


I gather you can't access Self in such methods.

Gareth aka. Kit


On Sat 28/07/18 20:37 , "Sven Barth" pascaldragon at googlemail.com <javascript:top.opencompose('pascaldragon at googlemail.com','','','')>  sent:

J. Gareth Moreton <gareth at moreton-family.com <mailto:gareth at moreton-family.com> > schrieb am Sa., 28. Juli 2018, 19:34:

I did wonder about that, but wasn't sure how it would affect things where inheritance is concerned.  I dare ask, do you have an example of a class method that you would consider pure?

 

They don't have inheritance. If they have the modifier "static" they really are simply scoped functions or procedures. They can even be assigned to non-"of object" procedure variables. 

 

Regards, 

Sven

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