[fpc-pascal] Re: Fpc Access Violation if AppConfigDir doesn't exist.

[Michael Van Canneyt]

On Wed, 13 Feb 2013, Giuliano Colla wrote:

> Sven Barth ha scritto:
>> On 13.02.2013 10:11, Lukasz Sokol wrote:
>>> On 13/02/2013 07:34, Michael Müller wrote:
>>> 
>>>> I'm not sure if somebody else mentioned this already but I have the 
>>>> feeling that Giuliano thinks that he has to decide to use try-finally OR 
>>>> try-except but there are situations where you need both. One of the 
>>>> criteria is if the object is local or global since for a global object it 
>>>> is likely that you place the .Free (or for a global object better 
>>>> FreeAndNil()) into a destructor or finalization section (which means that 
>>>> you have to stop the program in case of an error and not continue showing 
>>>> just a dialog) so you'll need only the try-except if you want to catch 
>>>> the exception. In case of a local object you'll ALWAYS have the lines
>>>> 
>>>> Obj := Class.Create;
>>>> try
>>>>    // do some code
>>>> finally
>>>>    Obj.Free;
>>>> end;
>>>> 
>>>> otherwise you'll end up with memory leaks.
>>>> If you want to catch the exception in this situation you'll put 
>>>> try-except extra around try-finally so you'll end up with
>>>> 
>>>> Obj := Class.Create;
>>>> try
>>>>    try
>>>>      // do some code
>>>>    finally
>>>>      Obj.Free;
>>>>    end;
>>>> except
>>>>    writeln('We have a problem);
>>>>    halt the program or reraise the exception or raise a new one
>>>> end;
>>>> 
>>>> Regards
>>>> 
>>> To developers:
>>> How would a generalized/packed construct like
>>> 
>>> try
>>> [code block]
>>> finally
>>> [code block]
>>> except
>>> [code block]
>>> end;
>> 
>> or what about
>> 
>> try
>> [code block]
>> except
>> [code block]
>> finally
>> [code block]
>> end;
>> 
>
> Python provides the following:
> try
> [code block]
> except
> [code block]
> else
> [code block]
> finally
> [code block]
> end;
>
> which can be used in any reasonable combination: just try..except, just 
> try..finally just try..except..else etc.
>
> The except..else is a very useful construct, because it provides a path to a 
> code block to execute only if there were no previous errors.
> This wouldn't break any existing applications, just add very useful features.
>
> What fpc developers think about that?

"Else" is used in Except already to select between various classes:

try
   ..
except
   on E : MyType do
     begin
     end
else
   // exception is not MyType
end;

so that is a problem.

I see no problem in adding finally, if you define carefully when it is executed.

Michael.