E2510 Type '%s' is not a valid constraint (Delphi)

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You cannot use a class reference as a type constraint in a generic class. Use a normal class instead.

program E2510;

{$APPTYPE CONSOLE}

uses
  SysUtils;

type
  TBaseType = class
  end;

  TBaseTypeClass = class of TBaseType;

  TFactory<T: TBaseTypeClass, constructor> = class //E2510 Fix: replace TBaseTypeClass with TBaseType
  end;

begin
  Writeln('FAIL - Type ''%s'' is not a valid constraint');
end.