New Warning in 12.2: Overloading a similar index type by declaring an array property 'Items'

[pyscripter 694]

The following code (from VirtualTrees) raises a new warning in Delphi 12.2:

  TVirtualTreeColumns = class(TCollection)
    ...

    property Items[Index : TColumnIndex] : TVirtualTreeColumn read GetItem write SetItem; default;
    ...

  end 

The warning says:

[dcc64 Warning] VirtualTrees.Header.pas(280): W1075 Overloading a similar index type by declaring an array property 'Items'
  VirtualTrees.Header.pas(280): Related member: property TVirtualTreeColumns.Items[TColumnIndex]: TVirtualTreeColumn;
  VirtualTrees.Header.pas(280): Related member: property TCollection.Items[Integer]: TCollectionItem;

I get quite a few similar warnings in my code base.

 

Clearly the overwriting (and not overloading) is intentional.    Any ideas of how to get rid of this warning without suppressing it?

 

Edited September 12 by pyscripter

[Anders Melander 1815]

1 hour ago, pyscripter said:

Any ideas of how to get rid of this warning without suppressing it?

You mean without using {$WARN}? Have you looked in the project settings to see if there's an option there to disable it?

[Uwe Raabe 2063]

AFAIK, there is no legal syntax to avoid this warning. The only way I know of is locally suppressing it:

    ...
{$WARN OVERLOADING_ARRAY_PROPERTY OFF}
    property Items[Index : TColumnIndex] : TVirtualTreeColumn read GetItem write SetItem; default;
   ...
 end;
{$WARN OVERLOADING_ARRAY_PROPERTY DEFAULT}

 

[pyscripter 694]

1 hour ago, Uwe Raabe said:

{$WARN OVERLOADING_ARRAY_PROPERTY OFF}

Will this not cause an issue with earlier DELPHI versions?

[Kas Ob. 121]

13 minutes ago, pyscripter said:

Will this not cause an issue with earlier DELPHI versions?

No issue there, just simple error.

Quote

[dcc32 Error] uMain.pas(74): E1030 Invalid compiler directive: 'OVERLOADING_ARRAY_PROPERTY'

 

[Angus Robertson 577]

I have the same problem with two units in ICS, so have added alternative NativeInt versions of the Items property for D12.2 and later.  

 

Angus

[pyscripter 694]

1 hour ago, Kas Ob. said:

No issue there, just simple error.

Great.   Swap a warning in 12.2 with an error in earlier versions.  

Edited September 12 by pyscripter

[pyscripter 694]

1 hour ago, Angus Robertson said:

have added alternative NativeInt versions of the Items property for D12.2 and later

Could you please give an example of what you did?

[Angus Robertson 577]

Assuming the warning relates to TList,Items[Index] changing from Integer to NativeInt, I created alternative versions of the SetItem and GetItem functions with NativeInt.

 

Our library needs to support older versions like 12.1 without warnings so DEFINES for 12.2 and later complicate it, you can probably just change a few Integers to NativeInt.

 

Angus

[pyscripter 694]

22 minutes ago, Angus Robertson said:

Assuming the warning relates to TList,Items[Index] changing from Integer to NativeInt, I created alternative versions of the SetItem and GetItem functions with NativeInt.

 

Our library needs to support older versions like 12.1 without warnings so DEFINES for 12.2 and later complicate it, you can probably just change a few Integers to NativeInt.

 

Angus

Aha!  So is the type of the indexed property that the compiler complains about and not just the fact that you overwrite the inherited indexed property!   And it is the change of Integer to NativeInt that caused that.

[pyscripter 694]

 

Interestingly the build dialog box reports this as 3 warnings!

 

Edited September 12 by pyscripter

[Jaska 7]

11 hours ago, Kas Ob. said:

No issue there, just simple error.

 

 

I use this to make code compatible to previous versions.

 

{$IFDEF VER360}
  {$IF Declared(RTLVersion122)}
    {$WARN OVERLOADING_ARRAY_PROPERTY OFF}
  {$IFEND}
{$ENDIF}
 

[Kas Ob. 121]

43 minutes ago, Jaska said:

{$IFDEF VER360}
  {$IF Declared(RTLVersion122)}
    {$WARN OVERLOADING_ARRAY_PROPERTY OFF}
  {$IFEND}
{$ENDIF}

This warning/error is here forever, i suggest to do yourself a favor and rewrite the above with future proof parameters.

[pyscripter 694]

7 hours ago, Kas Ob. said:

This warning/error is here forever, i suggest to do yourself a favor and rewrite the above with future proof parameters.

I ended up with the following, which is backward compatible and future proof:

    {$IF (CompilerVersion > 36) or Declared(RTLVersion122)}{$WARN OVERLOADING_ARRAY_PROPERTY OFF}{$ENDIF}
    property Items[Index : TColumnIndex] : TVirtualTreeColumn read GetItem write SetItem; default;
    property Header: TVTHeader read FHeader;
    property TrackIndex : TColumnIndex read FTrackIndex write FTrackIndex;
    property TreeView : TCustomControl read GetTreeView;
    property UpdateCount;
    {$IF (CompilerVersion > 36) or Declared(RTLVersion122)}{$WARN OVERLOADING_ARRAY_PROPERTY ON}{$ENDIF}
end;

Notes:

• If the $WARN OFF comes immediately after the Items declaration you still get the warning.
• Delphi 12.2 still defines RTLVersion121.  Presumably if there is a Delphi 12.3 etc.  RTLVersion122 will be defined.

Edited September 13 by pyscripter

[Lajos Juhász 295]

19 minutes ago, pyscripter said:

Delphi 12.2 still defines RTLVersion121.  Presumably if there is a Delphi 12.3 etc.  RTLVersion122 will be defined.

I have checked this on D11.2 there is also both RTLVersion111 and RTLVersion112 defined.

[Remy Lebeau 1427]

11 hours ago, Jaska said:

I use this to make code compatible to previous versions.

 

{$IFDEF VER360}
  {$IF Declared(RTLVersion122)}
    {$WARN OVERLOADING_ARRAY_PROPERTY OFF}
  {$IFEND}
{$ENDIF}
 

VER360 and RTLVersion12x are specific to the D12.x series and won't be declared anymore once D13.x+ is released.  So this is not future-proof.

 

Edited September 13 by Remy Lebeau

[pyscripter 694]

On 9/12/2024 at 9:16 PM, Angus Robertson said:

Assuming the warning relates to TList,Items[Index] changing from Integer to NativeInt, I created alternative versions of the SetItem and GetItem functions with NativeInt.

I am afraid is not that simple.   I did the same and when I tried to compile with Delphi 11 64bits, I got compilation errors, not in the declaration but when using the TObjectList descendent.   

 

Apparently Delphi implicitly supports indexed property overloading!  Hence the name of the warning.    Did you know that?  I didn't.

Example:

 

  TSynEditMarkList = class(TObjectList)

    ...
    function IsBookmark: Boolean;
    property Items[Index: NativeInt]: TSynEditMark read GetItem write SetItem; default;
  end;
  
  MarkList: TSynEditMarkList;
  
  var 
    I: Integer;
    J: NativeInt
    
    // Both indexed properties, the one defined here and the inherited one can be used as default properties.
    Mark[I].IsBookmark; //  error message IsBookmark is not recognized.  Mark[I] is a TObject as in the inherited class.
    Mark[J].IsBookmark; // works
    

 

I will probably end up using a generic TList to avoid this mess.

Edited September 14 by pyscripter

[Uwe Raabe 2063]

1 hour ago, pyscripter said:

Did you know that?

Yep! I first made use of that almost 10 years ago in a class holding translation strings. Before that the strings were indexed by an Integer, but later we extended that to string indices.

   property Items[Index: Integer]: string read GetItems; default;
   property Items[const Index: string]: string read GetItems; default;

The interesting part was that both are marked as default properties, which allowed us to simply write something like this:

Label1.Caption := Translations[42];
Label2.Caption := Translations['Error'];

The most benefit came from the fact that we could keep the Integer based translations and simply add the string based ones - all using the same Translations instance.

Edited September 13 by Uwe Raabe

[Angus Robertson 577]

Quote

I got compilation errors, not in the declaration but when using the TObjectList descendent. 

I only updated two ICS components derived from TList, not TObjectList with NativeInt, by creating a new {$DEFINE TListNatInt} for 12.2 and later, and then using conditional code, tested in 1.2 and 11.3, TObjectList may need a different approach. 

 

Angus

 

[pyscripter 694]

1 hour ago, Angus Robertson said:

{$DEFINE TListNatInt}

So, one approach is to do something like:

{$IF (CompilerVersion >= 35)
  TListSize = NativeInt;
{$ELSE}
  TListSize = Integer;
{$END}

 

and then something like:

 

  TSynEditMarkList = class(TObjectList)

    ...
    property Items[Index: TListSize]: TSynEditMark read GetItem write SetItem; default;
  end;

This would make sure that in all versions of Delphi you do not overload the array property but instead overwrite it.  Unintentionally overloading the array property is likely to cause trouble (see earlier post).  It also needs just one conditional compilation directive for the whole code base.

 

Edited September 14 by pyscripter

[Angus Robertson 577]

There are several ways of fixing the TList change, your conditional check would not work for Delphi 7 or Delphi 12.1, as has been explained earlier in this topic, and I prefer not to have too many special types in libraries, makes them harder to understand.  You also need to change the setters,

 

Angus

 

[Carlo Barazzetta 116]

22 hours ago, pyscripter said:

So, one approach is to do something like:

{$IF (CompilerVersion >= 35)
  TListSize = NativeInt;
{$ELSE}
  TListSize = Integer;
{$END}

 

and then something like:

 

  TSynEditMarkList = class(TObjectList)

    ...
    property Items[Index: TListSize]: TSynEditMark read GetItem write SetItem; default;
  end;

This would make sure that in all versions of Delphi you do not overload the array property but instead overwrite it.  Unintentionally overloading the array property is likely to cause trouble (see earlier post).  It also needs just one conditional compilation directive for the whole code base.

 

I'm using your suggestion, but using CompilerVersion>=36 (Delphi 12), so the correct syntax is:

{$IF (CompilerVersion >= 36)}TListSize = NativeInt;{$ELSE}TListSize = Integer;{$IFEND}

[Angus Robertson 577]

You still need   {$IF Declared(RTLVersion122)}  if you want the component to also work on 12.0 and 12.1.   And $IF is not supported on earlier compilers, if that matters.

 

Angus

 

[pyscripter 694]

1 hour ago, Angus Robertson said:

You still need   {$IF Declared(RTLVersion122)}  if you want the component to also work on 12.0 and 12.1.

No you don't.  The index was changed to NativeInt in Delphi 12.0.  There are no interface changes in minor versions. It is just the warning that was added in 12.2.

Regarding older versions,  you are right if you need to support versions before IF was introduced.  But many of us including @Carlo Barazzetta don't.

Edited September 15 by pyscripter

[Uwe Raabe 2063]

15 minutes ago, pyscripter said:

if you need to support versions before IF was introduced

IIRC, that has been Delphi 6 or 7. One can even test for that with {$IF CONDITIONALEXPRESSIONS}.