How can I declare an array property?

Question

I constructed class system

  TTableSpec=class(Tobject)
  private
    FName : string;
    FDescription : string;
    FCan_add : Boolean;
    FCan_edit : Boolean;
    FCan_delete : Boolean;
    FFields : array[1..100] of TFieldSpec;
  public
    property Name: String read FName;
    property Description: String read FDescription;
    property Can_add : Boolean read FCan_add;
    property Can_edit : Boolean read FCan_edit;
    property Can_delete : Boolean read FCan_delete;
    property Fields : array read FFields;
  end;

Thus in TableSpec Fields property shall be the list of fields (I used TFieldSpec array). How to organize the list of fields (using or without using an array) as as a result of compilation I receive an error

[Error] Objects.pas(97): Identifier expected but 'ARRAY' found
[Error] Objects.pas(97): READ or WRITE clause expected, but identifier 'FFields' found
[Error] Objects.pas(98): Type expected but 'END' found
[Hint] Objects.pas(90): Private symbol 'FFields' declared but never used
[Fatal Error] FirstTask.dpr(5): Could not compile used unit 'Objects.pas'

Solution 1

Your line

property Fields : array read FFields;

is invalid syntax. It should be

property Fields[Index: Integer]: TFieldSpec read GetField;

where GetField is a (private) function that takes an integer (the Index) and returns the corresponding TFieldSpec, e.g.,

function TTableSpec.GetField(Index: Integer): TFieldSpec;
begin
  result := FFields[Index];
end;

See the documentation on array properties.

Solution 2

I agree the answer regarding INDEXED properties, given by Andreas, is the solution the poster is looking for.

For completeness, for future visitors, I'd like to point out that a property can have an array type, as long as the type is named. The same applies to records, pointers, and other derived types.

type
  tMyColorIndex = ( Red, Blue, Green );
  tMyColor = array [ tMyColorIndex ] of byte;

  tMyThing = class
    private
      fColor : tMyColor;
    public
      property Color : tMyColor read fColor;
  end;

Comments

[Wouter van Nifterick]

Unless you're certain that you'll need exactly 100 fields, I'd create a type like type TFields=Array of TFieldSpec and then specify the fields attribute as FFields:TFields.

[Wouter van Nifterick]

Renamed the title, and removed irrelevant code. We don't need to see the entire unit in order to pinpoint the problem here.

[CodesInChaos]

Are you sure you want a property with an array type, or rather an indexer?

[john_who_is_doe]

Yes, sorry thats escaped my attention. (: