Question

could someone explain to me what is the reason that when creating a generic class I must move my private constans to the interface section? This is killing my design, I don’t want others to see something that should be private.

unit Unit38;

interface

uses
  Generics.Collections;

type
  TSimpleClass<T> = class(TObject)
  private
    procedure DoSomethingInternal(const SomeString: string);
  public
    procedure DoSomething;
  end;

implementation

const
  MyString = 'some string'; //Why this must be public?

{ TSimpleClass<T> }

procedure TSimpleClass<T>.DoSomething;
begin
  DoSomethingInternal(MyString); //Compiler error
end;

procedure TSimpleClass<T>.DoSomethingInternal(const SomeString: string);
begin
  //-------
end;

end.

Thanks.

Answer 1

Same error in D2010, so the generics fixes of D2010 did not address this. It is a bug: http://qc.embarcadero.com/wc/qcmain.aspx?d=79747

Fixed in build 15.0.3863.33207. Which I think is XE

Another QC on this is: http://qc.embarcadero.com/wc/qcmain.aspx?d=78022 which involves an enum and is still open.

The documentation on the error isn’t very clear by the way. See:

E2506 Method of parameterized type declared in interface section must not use local symbol ‘%s’

It involves a class var in a generic class which cannot be assigned a literal (!) value in the class’ constructor, the fix being to parameretrize the constructor… No idea why, but I guess it has to do with a compiler limitation.