Encapsulating existing functions within a class without generating proxy code?

[jamie]

I am looking to make a number of related functions to live in a class or Record that already exists in the rtl, but I would like the name space be within a class, and I don't want the compiler to generate extra call code for this.

Below is a simple Class function that uses an Inline to call the sysutils.Now without it generating extra code, I simply want the compiler to call the original function when it gets accessed from the class.

 Is there a known way to do this directly in the Class/Record definition, like an "Alias" of some sort?
 

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4. {$modeswitch AdvancedRecords}
5.  
6. interface
7.  
8. uses
9.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, StdCtrls;
10.  
11. type
12. TTimeClass = Class
13.  Class Function Now:TDateTime;
14. end;
15.  
16.   { TForm1 }
17.  
18.   TForm1 = class(TForm)
19.     Button1: TButton;
20.     procedure Button1Click(Sender: TObject);
21.   private
22.  
23.   public
24.   end;
25.  
26. var
27.   Form1: TForm1;
28.  
29. implementation
30.  
31. {$R *.lfm}
32. Class Function TTimeClass.Now:TDateTime; Inline;
33. begin
34.  Result := SysUtils.Now;
35. end;
36.  
37. { TForm1 }
38.  
39. procedure TForm1.Button1Click(Sender: TObject);
40. begin
41.  Caption := DateTimeTostr(TTimeClass.Now);
42. end;
43.  
44. end.
45.  
46.  

P.S.
 I am trying to get projects to work between Delphi and Lazarus.

[Fibonacci]

I dont think so, you will need to make all that little inline functions

[TRon]

Is there a known way to do this directly in the Class/Record definition, like an "Alias" of some sort?

Well, you can do this:
 

Code: Pascal  [Select][+][-]

1. program test;
2.  
3. {$mode objfpc}{$H+}
4.  
5. uses
6.   classes, sysutils;
7.  
8. var
9.   // Custom version of sysutils.now, invoking original sysutils.now function
10.   // Drawbacks: no overloads, no intrinsics
11.   Now : function: TDateTime = @sysutils.now;
12.   RightStr : function(const S: string; Count: Integer): string = @sysutils.RightStr;
13.   Sleep : procedure(milliseconds: Cardinal) = @sysutils.sleep;
14.  
15. var
16.   SomeNow: TDateTime;
17.  
18. begin
19.   // For functions without parameters we need to explicitely
20.   // mention to invoke the function to avoid copying the
21.   // contents of the variable
22.   // This is not required in mode Delphi but atm it eludes me
23.   // what modeswitch (if any) changes that behaviour
24.   SomeNow := Now();
25.   writeln('now = ', DateTimeToStr(Now()));
26.  
27.   // Function with parameters
28.   writeln(RightStr('1234567890',1));
29.  
30.   sleep(10*1000);
31.   writeln('done');
32. end.
33.  

I assume you are able to figure out how to drop that into a class/record ?

[Fibonacci]

// This is not required in mode Delphi but atm it eludes me
// what modeswitch (if any) changes that behaviour

Code: Pascal  [Select][+][-]

1. {$modeswitch CLASSICPROCVARS}  // tp style procvars (no @ needed)
2. {$modeswitch POINTERTOPROCVAR} // allows the assignement of pointers to procedure variables
3.  
4. uses SysUtils;
5.  
6. var
7.   Now: function: TDateTime = @SysUtils.Now;
8.  
9. begin
10.   writeln('Now = ', DateTimeToStr(Now));
11. end.

Code: Pascal  [Select][+][-]

1. {$modeswitch CLASSICPROCVARS}  // tp style procvars (no @ needed)
2.  
3. uses SysUtils;
4.  
5. var
6.   Now: function: TDateTime = SysUtils.Now;
7.  
8. begin
9.   writeln('Now = ', DateTimeToStr(Now));
10. end.

BTW, I dont like this in Delphi, assigning procedures/functions like that. It looks like the returned value should be assigned, not the function. With @ its obvious.

[TRon]

Splendid !

Thank you very much for that addition Fibonacci.

btw: for 3.2.2 it seems that modeswitch autoderef is also required.

BTW, I dont like this in Delphi, assigning procedures/functions like that. It looks like the returned value should be assigned, not the function. With @ its obvious.

I fully agree as for me it reads ambiguous. The way FPC does it makes it clear and indeed obvious.

[jamie]

let's not get carried away with this now

I just thought it to be nice to group a set of preexisting functions within a class/Record to make the code more manageable but not generate extra bloat over this.

 something like the TPath in Delphi is an example but I don't know if those members are directly linked to RTL functions or are proxy to some of them? But the concept is there to keep things cleaner.

 Also, one could make a record with some inner variables to localize some of the operations in specific code frags.

[TRon]

I just thought it to be nice to group a set of preexisting functions within a class/Record to make the code more manageable but not generate extra bloat over this.

You and me seem to have a different interpretation of what bloat means 

something like the TPath in Delphi is an example but I don't know if those members are directly linked to RTL functions or are proxy to some of them? But the concept is there to keep things cleaner.

Then have a look at how TPath is implemented ?

[jamie]

I never had any intention of duplicating the Tpath class, that was just an example which is very poorly done since most of those functions already exist in the RTL anyways, so the idea was to simply get the compiler to make a direct call instead of the proxy.

 I don't think Delphi is smart enough to make a direct call like that.

also on the other hand, any class functions that do not exist in the RTL can be tinkered with.

I have not tried using INLINE with Delphi yet to see if that actually works to shrink things down but a few tests with fpc shows that it's capable of reducing proxy calls.

Have fun.

[TRon]

I don't think Delphi is smart enough to make a direct call like that.

No it does not, or at least didn't (I more or less stopped following the progress of Delphi after that unpronounceable named company took over).

But that is imho besides the point. Whether the compiler has some nice trick up it sleeves to do as you want does not matter as behind the scenes it would have to do exactly the same as shown. It is the normal way to setup a jump table (that what you refer to as proxy) that can be used to plug-and-pray. There can be found many of such plug&play 'tables' in the FPC tree.

The only other way I am aware of, but being even more ugly and for sure more bloated, is that you can lookup the addresses and the parameter list using debug info (can probably be done using (extended) rtti as well). Some scripting languages seem to be using the rtti route to locate the required information.

You could always try a feature request though I am not sure it would serve enough purpose for it to be justified (in the eyes of the judges).