Board index » delphi » Re: Hejlsberg on language design

2003-10-12 02:10:55 AM
delphi32
Ingvar Nilsen writes:
try
// do something
except
end;
There may be a very rare exceptions <g>where this (suppression without
action) is justified, for example when dealing with some external process
you have no control over. But even then, chances are there is *something*
that should be done within such an exception. Also, as Anders points out,
exceptions are often handled at a local area when they should be allowed to
percolate up, in most cases at least, to a higher level, centralized,
exception handler.
try
// do something
SomeResource.Free;
except
SomeResource.Free;
end;
... or even ...
try
// do something
success := True;
except
SomeResource.Free;
Exit;
end;
if success then
SomeResource.Free;
I saw stuff like this all over a project I took over, recently written by a
company claiming to have Delphi expertise since D1. There should be no
exception blocks here, only finally blocks.
--
Wayne Niddery - Logic Fundamentals, Inc. (www.logicfundamentals.com)
RADBooks: www.logicfundamentals.com/RADBooks.html
"It is error alone which needs the support of government. Truth can
stand by itself." - Thomas Jefferson
 

Wayne Niddery [TeamB] writes:
not anymore.
That depends on what "handled" in this context means.
Resources allocated in the function block definitely need to be taken
care of by the local exception handler.
--
Ingvar Nilsen
 

Ingvar Nilsen writes:
function IsNumeric (const s : string) : boolean;
begin
try
Result := true;
IntToStr (s);
except
Result := false;
end;
end;
Wien.
 

Erwien Saputra writes:
--
Ingvar Nilsen
 

"Peter Sleuth" wrote
"But that said, there's certainly tremendous value in knowing what
exceptions can get thrown, and having some sort of tool that checks. [...] I
think we can certainly do a lot with analysis tools that detect suspicious
code, including uncaught exceptions, and points out those potential holes to
you".
Now go have a long hard look at QC #1556,
"Design-time utility to track exception propagation paths".
And please up your ratings, Hejlsberg (the father of Delphi) condones it
<g>!!!
Kristofer
 

Ingvar Nilsen writes:
examples, or why that code is bad?
If you are asking for other examples, another that I have in mind:
repeat
SomeVar := false;
try
qrySomething.Post;
SomeVar := true;
except
qrySomething.Cancel;
end;
until SomeVar = true;
I think those are example of abusing exception.
Wien.
 

"Rudy Velthuis (TeamB)" <XXXX@XXXXX.COM>writes
Chris Burrows
CFB Software
www.cfbsoftware.com
 

except that they do, the value in the exception. Life would be a bit
simpler if Post returned an error status one could use, otherwise using
exceptions to capture it is the only thing we can do. Your previous example
was in some ways a poor way to test for a number, but in other ways a good
way, since it ensured that the function conformed to the definition of the
IntToStr function, without attempting to duplicate it (or even worse,
failing to duplicate it).
Oliver Townshend
 

Ingvar Nilsen writes:
proper use. But it seems many never learn it.
for cleaning up resources. In most cases you don't need an exception block
at all, just a finally:
sl := TSomeObject.Create;
try
// do stuff that may cause exception
finally
sl.Free;
end;
The allocated object will always be properly freed whether there is an
exception or not.
Even if you handle the some or all exceptions here, it should be:
sl := TSomeObject.Create;
try
try
// do stuff that may cause exception
except
on e:SomeException do
begin
// do something about exception
end;
end;
finally
sl.Free;
end;
--
Wayne Niddery - Logic Fundamentals, Inc. (www.logicfundamentals.com)
RADBooks: www.logicfundamentals.com/RADBooks.html
"It is error alone which needs the support of government. Truth can
stand by itself." - Thomas Jefferson
 

Ingvar Nilsen writes:
this, it takes time and resources. In this example, you can use the good old
Pascal Val function and check the error code (that's actually what StrToInt
does anyway).
--
Wayne Niddery - Logic Fundamentals, Inc. (www.logicfundamentals.com)
RADBooks: www.logicfundamentals.com/RADBooks.html
"It is error alone which needs the support of government. Truth can
stand by itself." - Thomas Jefferson
 

 

Oliver Townshend writes:
fails, then repeating it like in this example isn't going to help.
--
Wayne Niddery - Logic Fundamentals, Inc. (www.logicfundamentals.com)
RADBooks: www.logicfundamentals.com/RADBooks.html
"It is error alone which needs the support of government. Truth can
stand by itself." - Thomas Jefferson
 

 

"Ingvar Nilsen" <XXXX@XXXXX.COM>writes
validation. This is lazy coding. If you want drive me ape-shit, just make
me debug somebody elses app where an exception is thrown constantly in some
kind of iteration loop, where the above example is THE RULE not the
EXCEPTION.
Its lazy. Exceptions should not be thrown as an expected outcome of what is
actually validation logic...