If the absence of dereferencing is the most important thing to you, you
could do something like this:
program Example;
{$mode ObjFPC}{$H+}
{$modeswitch AdvancedRecords}
type
TVec2 = record
X, Y: Integer;
end;
TVec2Array = array of TVec2;
TVecArray = record
strict private
Values: TVec2Array;
public
class function Create(const ACapacity: Integer = 16): TVecArray;
inline; static;
procedure Resize(const NewLength: Integer); inline;
property I: TVec2Array read Values write Values;
end;
class function TVecArray.Create(const ACapacity: Integer = 16): TVecArray;
begin
Result := Default(TVecArray);
SetLength(Result.Values, ACapacity);
end;
procedure TVecArray.Resize(const NewLength: Integer);
begin
SetLength(Values, NewLength);
end;
begin
with TVecArray.Create(0) do
begin
Resize(1);
I[0].X := 100;
I[0].Y := 100;
end;
end.
The only downside there is that you obviously don't quite get the real
"default" property syntax.
On Wed, Oct 10, 2018 at 11:06 PM Ryan Joseph
wrote:
> I’d like to know if there is a solution to the problem of indexing into
> records using [] properties.
>
> In the example below I have an array of records (a dynamic array for the
> example) and I’d like to use the [] property to index into the values. The
> problem is because the array holds records I need to return a pointer to
> the record so I can access the fields. In the end the only problem is I
> need to dereference the pointer using ^.
>
> Are there any solutions we could propose to this? Some ideas:
>
> 1) I looks like we could have a “var” modifier for function results but
> that concept has only ever existed in function params (like & in C++).
>
> function GetValue(i: integer): TVec2; var;
>
> 2) Maybe a modifier added to GetValue which tells the compiler to call the
> function (and result) like a pointer when the indexer is used?
>
>
>
> type
> TVec2 = record
> x, y: integer;
> end;
> TVec2Ptr = ^TVec2;
> TVec2Array = array of TVec2;
>
> type
> TVecArray = class
> values: TVec2Array;
> function GetValue(i: integer): TVec2Ptr;
> procedure Resize(newLength: integer);
> property Indexer[i: integer]: TVec2Ptr read GetValue;
> default;
> end;
>
>
> function TVecArray.GetValue(i: integer): TVec2Ptr;
> begin
> result := @values[i];
> end;
>
> procedure TVecArray.Resize(newLength: integer);
> begin
> SetLength(values, newLength);
> end;
>
> var
> arr: TVecArray;
> begin
> arr := TVecArray.Create;
> arr.Resize(1);
> arr[0]^.x := 100;
> arr[0]^.y := 100;
> end.
>
> Regards,
> Ryan Joseph
>
> ___
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> http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
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