Is there a procedure to initialize a variable number of objects at
runtime?
lazarus / 38-Networking and Web Programming

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vfclists · 2013-12-23 00:46

Is there a procedure to initialize a variable number of objects at
runtime in a single procedure?

I usually have initialize some variables like the TStringList type at
the start of procedures and free them afterwards.It feels awkward to
initialize the separately, like

Code: [Select]listOne := TStringList.Create;
listTwo := TStringList.Create;
listTree := TString.Create;{ etc, etc}

I would prefer a procedure like, with another for Free ing them a the
end:

Code: [Select]CreateStrings(listOne, listTwo, listThree);
CreateStrings([listOne, listTwo, listTree]); //using an array
Is there a procedure that can do something like this for a variable
number of objects?

If it can't be done for arbitrary object types, then at least  types
with the same Create signature?

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User137 · 2013-12-23 09:20

It's possible create such functions. But first thing you need to
decide is if they are all exactly TStringList type, or all kinds of
TStrings variants, because that would complicate it? For freeing i'm
thinking you could return an array reference from the creating
function, so you don't need to specify each object for freeing
procedure.

I don't remember exactly now if var typed array parameter can be
written into, propably not. You might have to give array of pointer to
each object. Here is some untested code:
Code: [Select]type
  TObjectArrayRef = array of TObject;
...
function CreateStringLists(var vars: array of TStringList):
TObjectArrayRef;
var i: integer;
begin
  setlength(result, length(vars));
  for i:=low(oArray) to high(oArray) do begin
    vars[i]:=TStringList.Create;
    result[i]:=vars[i];
  end;
end;

function CreateObjects(var vars: array of TObject; vTypes: array of
classType): TObjectArrayRef;
// Was it "classtype"? That answer can be found here on forums
var i: integer;
begin
  setlength(result, length(vars));
  for i:=low(oArray) to high(oArray) do begin
    vars[i]:=vTypes[i].Create;
    result[i]:=vars[i];
  end;
end;

procedure FreeObjects(oArray: TObjectArrayRef);
var i: integer;
begin
  for i:=low(oArray) to high(oArray) do
    oArray[i].Free;
end;
And of course doing procedures like this will slow down the program  
But if it's easier for the programmers eye then be my guest.

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vfclists · 2013-12-23 11:29

Can the admins move this topic to the General forum. I posted it this
forum accidentally?

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vfclists · 2013-12-23 11:32

Thanks for the examples. I will try them out.

In this case I prefer readability over speed.

Quote from: User137 on December 23, 2013, 10:20:00 amIt's possible
create such functions. But first thing you need to decide is if they
are all exactly TStringList type, or all kinds of TStrings variants,
because that would complicate it? For freeing i'm thinking you could
return an array reference from the creating function, so you don't
need to specify each object for freeing procedure.

I don't remember exactly now if var typed array parameter can be
written into, propably not. You might have to give array of pointer to
each object. Here is some untested code:
Code: [Select]type
  TObjectArrayRef = array of TObject;
...
function CreateStringLists(var vars: array of TStringList):
TObjectArrayRef;
var i: integer;
begin
  setlength(result, length(vars));
  for i:=low(oArray) to high(oArray) do begin
    vars[i]:=TStringList.Create;
    result[i]:=vars[i];
  end;
end;

function CreateObjects(var vars: array of TObject; vTypes: array of
classType): TObjectArrayRef;
// Was it "classtype"? That answer can be found here on forums
var i: integer;
begin
  setlength(result, length(vars));
  for i:=low(oArray) to high(oArray) do begin
    vars[i]:=vTypes[i].Create;
    result[i]:=vars[i];
  end;
end;

procedure FreeObjects(oArray: TObjectArrayRef);
var i: integer;
begin
  for i:=low(oArray) to high(oArray) do
    oArray[i].Free;
end;
And of course doing procedures like this will slow down the program  
But if it's easier for the programmers eye then be my guest.