按默认值创建一个常量的TDictionary数组

Question

I want to use the a TDictionary in a Delphi project. But I've a problem,how i can Create a constant array of TDictionary by default value ?

For example i want to allocate 4 item for a dictionary such as bellow code (for constant array of TItem ) :

...
type
  TItem = record
    _Key: string;
    _Value: string;
  end;
var
  Dic: array [0..3]of TItem=(
  (_Key:'A' ; _Value:'Apple'),
  (_Key:'B' ; _Value:'Book'),
  (_Key:'C' ; _Value:'C++'),
  (_Key:'D' ; _Value:'Delphi')
  );
...

Is there any way to do this work with TDictionary ? I want to create a constant array of Dic (but) such as bellow structure .

  ...
    var
      Dic: TDictionary<string, string>;
    begin
      Dic := TDictionary<string, string>.Create;
      try
        Dic.Add('A', 'Apple');
        Dic.Add('B', 'Book');
        Dic.Add('C', 'C++');
        Dic.Add('D', 'Delphi');
      finally
         ///
      end;
    ...

Anyone have any advice for me? (Excuse me if my English is poor !)

Answer 1

You cannot write a constant expression that is an instance of a class.

Yet, since your TDictionary is a collection of String which is a type that you can create constants with, you could just build your TDictionary at run time from your constants. You could use records as in your question, but I like arrays:

{$IFDEF WHATEVER}
type
  TDictConstant = array[0..3, 0..1] of String;
const
  DICT_CONSTANT: TDictConstant = (('A', 'Apple'), ('B', 'Book'), ('C', 'C++'), ('D', 'Delphi'));
{$ELSE}
// If you want it "blank" for one config
type
  TDictConstant = array[0..0, 0..1] of String;
const
  DICT_CONSTANT: TDictConstant = (('', ''));
{$ENDIF}
var
  Dic: TDictionary<string, string>;

procedure TForm1.FormCreate(Sender: TObject);
var
  i: Integer;
begin
  Dic := TDictionary<string, string>.Create;
  for i := 0 to High(DICT_CONSTANT) do
  begin
    // Ignore the "blank" ones
    if (DICT_CONSTANT[i][0] <> '') or (DICT_CONSTANT[i][1] <> '') then
    begin
      Dic.Add(DICT_CONSTANT[i][0], DICT_CONSTANT[i][1]);
    end;
  end;
end;

I've done similar in the past.

Answer 2

You cannot write a constant expression that is an instance of a class. So what you are attempting to do is not possible.