[dcc32 Error] Type parameter 'T' must be a non-nullable value type

[EugeneK 22]

Hi

 

Anyone else have this error in 12.3

[dcc32 Error] Type parameter 'T' must be a non-nullable value type

Works fine in 12.2, trying to isolate it now, seems to work in some places but not the others.

[EugeneK 22]

Happens when record field has an attribute

unit UTestGenericsBug;

interface

uses
  System.Rtti,
  Data.DB;

type
  DBField = class(TCustomAttribute)
  strict private
    FFieldType: TFieldType;
    FLength: Integer;
  public
    constructor Create(const AFieldType: TFieldType = ftUnknown; const ALength: Integer = 0);
    property FieldType: TFieldType read FFieldType;
    property Length: Integer read FLength;
  end;

  TTestRecord = record
  private
    [DBField(ftString, 20)]
    FTerminalName: string;
  public
  end;

  TRecordLoader<T: record> = class sealed
    class function Get: T; static;
  end;

implementation

constructor DBField.Create(const AFieldType: TFieldType = ftUnknown; const ALength: Integer = 0);
begin

end;

class function TRecordLoader<T>.Get: T;
begin
  Result := Default(T);
end;

function Get: TTestRecord;
begin
  // error here
  Result := TRecordLoader<TTestRecord>.Get;
end;

end.

😒

[DelphiUdIT 214]

TRecordLoader<T> = class sealed
    class function Get: T; static;

If you use full generic declaration it works.

[EugeneK 22]

Just now, DelphiUdIT said:

TRecordLoader<T> = class sealed
    class function Get: T; static;

If you use full generic declaration it works.

Yes I'll probably use it as a workaround, but that kind of defeats the purpose