Returning a dynamic array from a function - arrays

Question

I'm working with Delphi 7.
Here's my base class. The function load_for_edit() is supposed to return an array of strings which sounds like it does. The problem is not particularly here but further.
...
type
TStringArray = array of string;
...
function load_for_edit(): TStringArray;
...
numberOfFields: integer;
...
function TBaseForm.load_for_edit(): TStringArray;
var
query: TADOQuery;
i: integer;
begin
query := TADOQuery.Create(self);
query.Connection := DataModule1.ADOConnection;
query.SQL.Add('CALL get_' + self.table_name + '_id(' + self.id + ')');
query.Open;
numberOfFields := query.Fields.Count;
SetLength(result, query.Fields.Count);
for i := 0 to query.Fields.Count - 1 do
result[i] := query.Fields[i].Value.AsString;
end;
Next is the class that is a descendant of the base class and it's trying to receive an array from the base class's load_for_edit() function.
...
type
TStringArray = array of string;
...
procedure TPublisherEditForm.FormShow(Sender: TObject);
var
rec: TStringArray;
begin
inherited;
SetLength(rec, self.numberOfFields);
rec := load_for_edit(); // Compilation stops here
end;
But, the application won't compile. Delphi spits out this error message:
Incompatible types
So, what this means is that the function load_for_edit() returns a data type that is different from the variable rec's data type, though, as can be seen from their respective type declaration sections, their declarations are absolutely identical. I don't know what's going on here and what to do. Please, help me come up with a solution.

Answer 1

You've got two separate declarations of TStringArray (one in each unit), and they are not the same. (The fact that they're in two separate units makes them different. UnitA.TStringArray is not the same as UnitB.TStringArray, even if they're both declared as type TStringArray = array of string;.)
You need to use a single type declaration:
unit
BaseFormUnit;
interface
uses
...
type
TStringArray: array of string;
TBaseForm = class(...)
numberOfFields: Integer;
function load_for_edit: TStringArray;
end;
implementation
// Not sure here. It looks like you should use a try..finally to
// free the query after loading, but if you need to use it later
// to save the edits you should create it in the TBaseForm constructor
// and free it in the TBaseForm destructor instead, which means it
// should also be a field of the class declaration above.
function TBaseForm.load_for_edit(): TStringArray;
var
query: TADOQuery;
i: integer;
begin
query := TADOQuery.Create(self);
query.Connection := DataModule1.ADOConnection;
query.SQL.Add('CALL get_' + self.table_name + '_id(' + self.id + ')');
query.Open;
numberOfFields := query.Fields.Count;
SetLength(result, numberOfFields);
for i := 0 to numberOfFields - 1 do
Result[i] := query.Fields[i].Value.AsString;
end;
...
end.
Now your descendant class can access it:
unit
PublisherEditFormUnit;
interface
uses
... // Usual Forms, Windows, etc.
BaseFormUnit;
type
TPublisherEditForm = class(TBaseForm)
...
procedure FormShow(Sender: TObject);
end;
implementation
procedure TPublisherEditForm.FormShow(Sender: TObject);
var
rec: TStringArray;
begin
// No need to call SetLength - the base class does.
rec := load_for_edit(); // Compilation stops here
end;
...
end.