[DUG] Dumb Friday Question

Fri May 4 17:55:40 NZST 2007

Hi C(K)arl,

Sure PopulateList could be in the try finally block (probably better in
a nested except block actually), but the rest of what you say does not
make sense for this function. Perhaps you are mixing up the 2 different
functions?

I purposely didn't add exception handling to the examples, as I wanted
to more clearly illustrate the class creation point. Obviously all solid
code should also have the appropriate exception handling. 

Cheers Tim.

________________________________

From: delphi-bounces at delphi.org.nz [mailto:delphi-bounces at delphi.org.nz]
On Behalf Of Karl Reynolds
Sent: Friday, 4 May 2007 3:00 PM
To: 'NZ Borland Developers Group - Delphi List'; vss at vss.co.nz
Subject: RE: [DUG] Dumb Friday Question

It isn't different, but that's because:

List := TStringList.Create;

 PopulateList(List);    

try

  if List.Count > 0 then

  begin

     ...do lots of stuff with the list

  End;

Finally

  List.Free;

End;

is not safe. You need to move the PopulateList(List) inside the
try/finally, and therein lies the problem if you had encapsulated it
together with the TStringList.Create inside a function
(GetLoadsOfStrings). If you want to do things this way, you should make
GetLoadsOfStrings be a constructor instead (obviously you would have to
subclass TStringList to achieve this).

Cheers,

Carl

________________________________

From: delphi-bounces at delphi.org.nz [mailto:delphi-bounces at delphi.org.nz]
On Behalf Of Tim Jarvis
Sent: Friday, May 04, 2007 4:30 PM
To: NZ Borland Developers Group - Delphi List; vss at vss.co.nz
Subject: RE: [DUG] Dumb Friday Question

Hi Guys,

Hope you don't mind me sticking my nose in here. Firstly I agree with
the sentiment that you should try and avoid creating objects in one
place and freeing in another, however I don't think that this situation
represents that, think of a function that returns a class as a factory
method, these obviously are quite common and not bad practice at all, in
fact a constructor is a factory type method.

Procedure DoSomthing;

Var

  List : TStrings;

Begin

List := GetLoadsOfStrings;

try

  if assigned(List) then

  begin

     ...do lots of stuff with the list

  End;

Finally

  List.Free;

End;

End;

Is really not much different from 

Procedure DoSomthing;

Var

  List : TStrings;

Begin

List := TStringList.Create;

 PopulateList(List);    

try

  if List.Count > 0 then

  begin

     ...do lots of stuff with the list

  End;

Finally

  List.Free;

End;

End;

The issue is where the variable is declared, and the scope of the
ownership not the act of creation, creation is fine to delegate to a
factory type method.

Regards Tim.

________________________________

From: delphi-bounces at delphi.org.nz [mailto:delphi-bounces at delphi.org.nz]
On Behalf Of Rohit Gupta
Sent: Friday, 4 May 2007 12:22 PM
To: vss at vss.co.nz; NZ Borland Developers Group - Delphi List
Subject: Re: [DUG] Dumb Friday Question

I would go along with Robert, you should not return complex types from
functions that create them,   It makes the code messy, you create it in
one place and free it in another.  Any sort of code analyser would also
complain about this.  You could return a string = stringlist.text and
assign it to a local stringlist.

Jeremy Coulter wrote: 

Hi All. This is a question that might be infulenced by some serious lack
of sleep :-)

I have a funtion. Its return result is a TStringlist.

In my code I create a TStringlist then add my values to it, then pass
this to the RESULT varaible for the function.

Now,  this is prob. an obvious answer than I prob. do actually know, but
if I got:-

sResult := TStringList.create;

sResult.add('blah');

Result:=sResult;

Then if I free sResult, then I loss the values I added, and the result
is empty as you would expect.

But the issue I have is, so if I DONT free sResults, what happens to it?
Surley it stays in memory,a dn I would end up with a memory leack after
repeaditive calls. Is that right? Or is because the variable is function
specific its free by default etc?

Its a basic question I know....but the more I thought about it the more
uncertain I became....I really need some sleep so that prob. the real
probelm :-)

Jeremy

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Rohit Gupta

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