[DUG] Dumb Friday Question

[Karl Reynolds]

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

B.E. Elec.   M.E.   Mem IEEE    Associate IEE

Technical Manager

Computer Fanatics Limited

 

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Email   <mailto:rohit at cfl.co.nz> rohit at cfl.co.nz

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