Interface problem

[mikerabat]

I have a bit of a delicate problem...

This idea compiles in Delphi well:

Code: Pascal  [Select][+][-]

1. program project1;
2.  
3. {$mode Delphi}{$H+}
4.  
5. uses
6.   {$IFDEF UNIX}
7.   cthreads,
8.   {$ENDIF}
9.   Classes, SysUtils, CustApp
10.   { you can add units after this };
11.  
12. type
13.   IBaseIntf = interface
14.   ['{99B2F4ED-0F79-47BD-8F77-594CD26C5FD1}']
15.     function TestBase( a : integer ) : integer;
16.   end;
17.  
18. type
19.   IDerriveIntf = interface(IBaseIntf)
20.   ['{C9C458E1-EB08-45ED-B7DE-EA9FBF3ADFD3}']
21.     function TestDerrive(a : integer) : Integer;
22.   end;
23.  
24. type
25.  
26.   { TBaseClass }
27.  
28.   TBaseClass = class(TInterfacedObject, IBaseIntf)
29.   protected
30.     function IBaseIntf.TestBase = TestBaseI;
31.     function TestBaseI( a : integer ) : integer;
32.   end;
33.  
34. type
35.  
36.   { TDerrivedClass }
37.  
38.   TDerrivedClass = class(TBaseClass, IDerriveIntf)
39.   protected
40.     function TestDerrive(a : integer) : Integer;
41.   end;
42.  
43. type
44.  
45.   { TIntfTestApp }
46.  
47.   TIntfTestApp = class(TCustomApplication)
48.   protected
49.     procedure DoRun; override;
50.   public
51.   end;
52.  
53. { TBaseClass }
54.  
55. function TBaseClass.TestBaseI(a: integer): integer;
56. begin
57.      Result := a - 4;
58. end;
59.  
60. { TDerrivedClass }
61.  
62. function TDerrivedClass.TestDerrive(a: integer): Integer;
63. begin
64.      Result := a + 4;
65. end;
66.  
67. { TIntfTestApp }
68.  
69. procedure TIntfTestApp.DoRun;
70. var
71.   ErrorMsg: String;
72.   a : IDerriveIntf;
73.   b : IBaseIntf;
74. begin
75.    a := TDerrivedClass.Create;
76.    Writeln(a.TestDerrive(44));
77.    Writeln(a.TestBase(44));
78.    b := TBaseClass.Create;
79.    Writeln(b.TestBase(44));
80.  
81.    readln;
82.  
83.   // stop program loop
84.   Terminate;
85. end;
86.  
87. var
88.   Application: TIntfTestApp;
89. begin
90.   Application:=TIntfTestApp.Create(nil);
91.   Application.Title:='Interface Test';
92.   Application.Run;
93.   Application.Free;
94. end.
95.  

And by idea I mean that there is a base interface def, a derrived one that includes the base interface and two classes that implement these interfaces.
Note that I need some kind of delegation in the base class in the form
IBaseIntf.TestBase = TestBaseI

In this case - if I have a delegating declaration like this the compiler starts to mock and throws an "this is not implemented" error. My problem is that this compiles in Delphi :/ . Is there anything that I can do in that regard? How can I fix the compile error - without removing the "delegation" stuff.

Background is that:
* I want to have a generic base matrix interface and class
* 2 derrived classes for complex and real valued matrices
* 2 derrived interfaces that implement complex and double valued matrices with the overlap of generic (IMatrix) functions that sometimes are also are superseeded (with the same name) in the derrived classes.

Note that the delphi implementation on github.com/mikerabat/mrmath already does all these things but I'm stuck now with the FPC stuff :/

Is there anything I can do in that regard?

kind regards
  Mike

[LeP]

By now, I think you have to insert a duplicate declaration of TestBase:

Code: Pascal  [Select][+][-]

1. type
2.  
3.   { TDerrivedClass }
4.  
5.   TDerrivedClass = class(TBaseClass, IDerriveIntf)
6.   protected
7.     function IDerriveIntf.TestBase = TestBaseI; <--------------------
8.     function TestDerrive(a : integer) : Integer;
9.   end;

I don't know if that works but I think FPC wants that.

[jamie]

I tried his code in an older version of delphi and good basically the same error.

Maybe newer versions work this out.

[LeP]

I install Lazarus now (4.6) and I try the original code and doesn't works, but it works in the last Delphi release.

Adding what I write in my post make the code working in Lazarus.

The original code can be used only in case expresses by OP, cause if you have (for example) the overload methods in the interface you cannot inherited the functions through a delegation.

[mikerabat]

I used the delegation method especially because there are overloaded functions so I do not have introduce casts as much. They should be automatically handled by the compiler
(and in theory there is no ambiguity). But it seems I cannot do this this here...

[LeP]

I used the delegation method especially because there are overloaded functions so I do not have introduce casts as much. They should be automatically handled by the compiler
(and in theory there is no ambiguity). But it seems I cannot do this this here...

At that time I think that for what you needs the interface methods should supports generics or some some other compiler "magic".
But as a famous movie said, this is not the time.

Without delegation, there were no problems.

May be some other people can answer with more knowledge.

[PascalDragon]

Is there anything I can do in that regard?

As LeP said, you need to declare the method alias for IDerriveIntf as well.

Other than that, please report a bug with your example considering that it works in Delphi.

[Thaddy]

The original statement that it - the presented code - compiles in Delphi is incorrect. Frankly: false.
The code needs quite some changes to make it compile since Delphi does not know custapp.
(Tested D7 and D12 CE)

And when you eliminate the custapp use, it still only works with LeP 's modification.

And that is to be expected, since the first alias is an implementation alias and the second one is not automatically assigned from the use of the interface alone, so it also needs an implementation alias.

So LeP's code is the correct solution for BOTH Delphi and FPC.

[LeP]

The original statement that it - the presented code - compiles in Delphi is incorrect. Frankly: false.
The code needs quite some changes to make it compile since Delphi does not know custapp.
(Tested D7 and D12 CE)

And when you eliminate the custapp use, it still only works with LeP 's modification.

And that is to be expected, since the first alias is an implementation alias and the second one is not automatically assigned from the use of the interface alone, so it also needs an implementation alias.

So LeP's code is the correct solution for BOTH Delphi and FPC.

No, this is not right. Custom APP has nothing to do with the ISSUE. You can delete all custom app related and still have the ISSUE in Lazarus (FPC).
The original code works with Delphi (Custom App excluded of course), but also with "{$mode Delphi}{$H+}" excluded of course , and .... of course .....

[Thaddy]

I know that custapp has nothing to do with the issue, but it has to do with the original claim.
I tested that, removed custapp code, and it did NOT work in D7 or D12.CE without your modification.

[LeP]

I know that custapp has nothing to do with the issue, but it has to do with the original claim.
I tested that, removed custapp code, and it did NOT work in D7 or D12.CE without your modification.

Read better: LAST DELPHI RELEASE. I mean the official Delphi 13 Florence.

If you refer to old product (CE it's based as tech on April 2024, and released on August 2024) may be you are right.

[marcov]

I know that custapp has nothing to do with the issue, but it has to do with the original claim.
I tested that, removed custapp code, and it did NOT work in D7 or D12.CE without your modification.

Read better: LAST DELPHI RELEASE. I mean the official Delphi 13 Florence.

If you refer to old product (CE it's based as tech on April 2024, and released on August 2024) may be you are right.

I also removed the customapp ancestor, change run to dorun, and change create(NIL) to create() and it works in Seattle (Delphi 10.0), printing 48,40,40

The question if that is accident or not, is the question. Probably we would need tests that dump the interface tables.

I haven't used interfaces much in recent times, but I can remember from the old days that it was a kind of rule in FAQs and forums to always declare all interfaces in the final (to use) class. However that might be meant for cases where only IderriveIntf is declared, and where the ancestor interface must be explicitly named. It might not apply here since IBaseIntf is declared in an ancestor class.

[mikerabat]

I know that custapp has nothing to do with the issue, but it has to do with the original claim.
I tested that, removed custapp code, and it did NOT work in D7 or D12.CE without your modification.

Actually this is not true at all. I tested this code with D2010 and D13 - and frankly I do not expect a problem with D12:
here the adjusted - delphi compilable program.

Code: Pascal  [Select][+][-]

1. program Project1;
2.  
3. {$APPTYPE CONSOLE}
4.  
5. {$R *.res}
6.  
7. uses
8.   Classes,
9.   SysUtils;
10.  
11. type
12.   IBaseIntf = interface
13.   ['{99B2F4ED-0F79-47BD-8F77-594CD26C5FD1}']
14.     function TestBase( a : integer ) : integer;
15.   end;
16.  
17. type
18.   IDerriveIntf = interface(IBaseIntf)
19.   ['{C9C458E1-EB08-45ED-B7DE-EA9FBF3ADFD3}']
20.     function TestDerrive(a : integer) : Integer;
21.   end;
22.  
23. type
24.  
25.   { TBaseClass }
26.  
27.   TBaseClass = class(TInterfacedObject, IBaseIntf)
28.   protected
29.     function IBaseIntf.TestBase = TestBaseI;
30.     function TestBaseI( a : integer ) : integer;
31.   end;
32.  
33. type
34.  
35.   { TDerrivedClass }
36.  
37.   TDerrivedClass = class(TBaseClass, IDerriveIntf)
38.   protected
39.     function TestDerrive(a : integer) : Integer;
40.   end;
41.  
42. { TBaseClass }
43.  
44. function TBaseClass.TestBaseI(a: integer): integer;
45. begin
46.      Result := a - 4;
47. end;
48.  
49. { TDerrivedClass }
50.  
51. function TDerrivedClass.TestDerrive(a: integer): Integer;
52. begin
53.      Result := a + 4;
54. end;
55.  
56. { TIntfTestApp }
57.  
58. procedure DoRun;
59. var
60.   a : IDerriveIntf;
61.   b : IBaseIntf;
62. begin
63.    a := TDerrivedClass.Create;
64.    Writeln(a.TestDerrive(44));
65.    Writeln(a.TestBase(44));
66.    b := TBaseClass.Create;
67.    Writeln(b.TestBase(44));
68.  
69.    readln;
70.  
71. end;
72.  
73. begin
74.   DoRun;
75. end.
76.  

[PascalDragon]

And when you eliminate the custapp use, it still only works with LeP 's modification.

I had tested with Delphi 10.2 and after adjusting for CustApp related issues it compiled.