[Closed]Copy constructors being past as value to Function parameters.

[jamie]

Today I discovered that passing a record as value to a function will call the "Copy" Class Operator, in Delphi it's called the "Assign". This is good news, news I wish I knew earlier, which I believe did ask about but got a "I am not sure" answer, very understandable.

 I had thought I tested this before hand and concluded that it didn't call the COPY ( constructor ) when passing by value to a function but today, using 3.2.4, it seems I must of been incorrect or 3.2.4 has fixed this.

 I know it worked if doing a := between records.

Code: Pascal  [Select][+][-]

1. TTestRec = Record
2.   S :String;
3.  Class Operator Copy(Constref Src:TTestRec;var Dest:TTestRec);
4.  End;                                    
5.  

But I see either I missed that or it now works with VALUE parameters in 3.2.4

Jamie




 

[ALLIGATOR]

Code: Pascal  [Select][+][-]

1. program app;
2. {$mode objfpc}
3. {$h+}
4. {$modeswitch advancedrecords}
5.  
6. type
7.   TTestRec = record
8.     S: String;
9.     class operator copy(constref src: TTestRec; var dest: TTestRec);
10.   end;
11.  
12. class operator TTestRec.copy(constref src: TTestRec; var dest: TTestRec);
13. begin
14.   WriteLn('kek');
15. end;
16.  
17. procedure kek1(A: TTestRec);
18. begin
19. end;
20.  
21. procedure kek2(const A: TTestRec);
22. begin
23. end;
24.  
25. procedure test;
26. var
27.   L: TTestRec;
28. begin
29.   kek1(L);
30.   kek2(L);
31. end;
32.  
33. begin
34.   test;
35.   ReadLn;
36. end.

No "kek"

 

(FPC git[main])

[jamie]

the "Const" is causing that because the compiler picks a REF instead of VALUE and that does not trigger the Copy.

  The same in C++, if its passed by REF

Jamie

[ALLIGATOR]

I won't understand what the problem is - or if there even is one - at that point

[jamie]

There does not appear to be any problem, compiler should adjust ref count for managed types in the record if past via value, it was the COPY operator that seems to be alluding me but appears to be working now as I would expect.

Jamie