[fpc-pascal] using exceptions

[Marcos Douglas]

On Wed, Dec 21, 2011 at 10:29 PM,  <noreply at z505.com> wrote:
> Marcos wrote:
>> I use Exceptions to check the integrity of classes. I have one
>> Exception for each class (E<class_name>), most of the time.
>
>
> Another problem with errors is that sometimes it is hard for a class to
> return errors. In procedural programming you can usually return an error
> as a parameter but sometimes in class programming it is difficult for
> classes to just return errors.

It's not difficult, but is boring have always a parameter or function
return to return an error, and have to verify if error then... if not
error...  if error and error then... etc

> Exceptions are an attempt to solve the problem, but imo this still doesn't
> solve all problems and our applications are full of wild exceptions going
> off despite our attempts to solve the problem.. because people fail to
> check exceptions and catch them. usually I see code like this:
>
> Try
>
> Finally
>
>
> You don't see as much Try Except, it's more Try Finally. People ignore the
> exceptions because it's an accepted thing to do. Then the end user of the
> application gets a strange exception message instead of a user friendly
> one. For example, if a file is not found, I like to give a polite "Cannot
> find file" message.. but usually in delphi apps and examples all over the
> newsgroups you see just an EFileNotFound exception pop up instead. Or,
> with StrToInt, a similar obscure exception message to the end user instead
> of a more friendly one.

I use many try-except in my own code but, most of the time, just catch
my own exceptions because they are much more simpler to use. As I said
before, I have Exceptions in only 2 levels: user and Lib (API,
business rules, etc).
The User exceptions always show a user friendly message (I think that
you call Errors, right?). The Lib exceptions, for me, is the real
Exception. So, If I call a routine but the app is not connected on
DBMS... raise Exception; if a important property not been set... raise
Exception; if a file has not found, this is not a exception, but if
the app can not create a file... raise Exception.

Marcos Douglas