[fpc-devel] Property overloading vs. property array enumerators

[Anthony Walter]

Here is a preferable solution:

    property Controls: IControlEnumerator read GetItems;

This allows for both:

  for C in Test.Controls do ShowMessage(C.Name);
  // or
  for I := 0 to Test.Controls.Count - 1 do ShowMessage(Test.Controls[I]);

That is you can access the property as either an enumerable collection, or
and an indexed collection. Note it has support for a default indexer
property and a count property.

This is where where:

  IControlEnumerator = IIndexedEnumerator<TControl>;

And:

type
  IIndexedEnumerator<T> = interface(IEnumerator<T>)
    function GetEnumerator: IIndexedEnumerator<T>;
    function GetCount: Integer;
    function GetItem(Index: Integer): T;
    property Count: Integer read GetCount;
    property Item[Index: Integer]: T read GetItem; default;
  end;

And finally putting together Test object as a simple example. Note that
TTest has full private access to the underlying container FList:

type
  TTest = class
  private
    FList: TList<TControl>;
    function GetItems: IControlEnumerator;
  public
    constructor Create(Controls: array of TControl);
    destructor Destroy; override;
    property Controls: IControlEnumerator read GetItems;
  end;
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