!(How to best use a try catch block) [modified]

[singh iz king]

Just came across a class which has tens of such properties. These properties are called by other classes and by other properties / methods of this class!!! Oh! and also look how the property name says total, but is actually returning an average :omg:

public double CrappyTotal
{
double CrappyTotal = 0; // notice the name of the variable is the same as the property
try
{
CrappyTotal = this.SomeItem.Details[0].Value;
CrappyTotal += this.SomeItem.Details[1].Value;
CrappyTotal += this.SomeItem.Details[2].Value;
CrappyTotal += this.SomeItem.Details[3].Value;
CrappyTotal = CrappyTotal / 4;
}
catch
{
CrappyTotal = -1;
}
return CrappyTotal;
}

modified on Wednesday, July 8, 2009 11:35 PM

[killabyte]

what crappy code....

[josda1000]

would the path ever get into the catch block anyway? wow lol i think my eyes just burned out.

[molesworth]

What language is this? I thought it was C#, but there's no "get" or "set", and you can't declare local variables in a property.

There are three kinds of people in the world - those who can count and those who can't...

[Dan Neely]

this.SomeItem.Details = new double[3]; MessageBox.Show(this.CrappyTotal);

The European Way of War: Blow your own continent up. The American Way of War: Go over and help them.

[Andrew Rissing]

He probably forgot to include the get/set because he was altering the code to post it up here. As for not declaring local variables in properties, you can.

[molesworth]

Andrew Rissing wrote:

He probably forgot to include the get/set because he was altering the code to post it up here.

Ah, OK - I was a bit confused (it's been a long day).

Andrew Rissing wrote:

As for not declaring local variables in properties, you can.

Only inside a getter or setter, not as a "property local". I'm easily confused though... :)

There are three kinds of people in the world - those who can count and those who can't...

[0x3c0]

Perhaps he missed out the () at the end of the method name?

Between the idea And the reality Between the motion And the act Falls the Shadow

[supercat9]

If the total is expected to always be computable, but it would be better to return -1 than to throw an exception if it isn't, how would you suggest coding it? Testing all four values to see if they're valid, testing to see whether any of the values is so big as to risk overflow, etc. would seem more complicated than just catching an exception. To be sure, such an approach would yield better performance in the case where an exception would be thrown and caught, but worse performance in the expected case where the total can be computed without difficulty. With regard to the relative wisdom of returning -1 versus propagating the exception, that would depend upon what the calling program is going to do with the information. It's not hard to imagine situations where having the function return -1 will be much cleaner than having it throw an exception, and others where the reverse would be true. BTW, one thing I would think would be useful in many situations where some callers would like exceptions handled and others would like them stifled would be for a method to accept a delegate to be called in case of trouble. Such a delegate could throw an exception if necessary, but could also handle some "trouble" situations better than would an exception.

[Lost User]

Except that you don't get an error on overflow, you just get PositiveInfinity (or NegativeInfinity), so the only thing that could throw an exception there is the indexing of this.SomeItem.Details You'd just have to test the length/count of that thing, whatever it is..

[singh iz king]

Yup...rightly picked up. I forgot to include the get block :doh:

[Thomas Weller 0]

NEVER ever throw an exception to code a foreseeable condition - even if it might be rare. Exceptions are just not made for that, they are for error conditions! It's like knocking in a nail with a wrench: You might succeed somehow, but anyway this is hardly a good and recommendable practice...

supercat9 wrote:

how would you suggest coding it?

public double CrappyTotal // and yes, this 'Total' is an 'Average'
{
get
{
if (this.SomeItem.Details.Length < 4)
{
return -1;
}

    return (this.SomeItem.Details\[0\].Value +	
            this.SomeItem.Details\[1\].Value +		
            this.SomeItem.Details\[2\].Value +		
            this.SomeItem.Details\[3\].Value) / 4;
}

}

I really would feel ashamed to code this with an exception instead, it's just ugly and bad craftsmanship... Regards Thomas

www.thomas-weller.de Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.
Programmer - an organism that turns coffee into software.

[BadKarma]

If I see such a thing i can say only one thing: "Everybody please remain calm! You Sir!! Get your hands up in the air and step away from the keyboard!"

Learn from the mistakes of others, you may not live long enough to make them all yourself.

[singh iz king]

Hi Thomas, Thanks for that. The day I came across this, I had a private discussion with the developer and reasoned the right way of doing this. The message seems to be slowly getting across :)

[singh iz king]

Lol...good one Unfortunately, I've come across so many such instances of bad programmers in my career (and I'm sure most of you have as well). This fortunately for me has been the only instance where the developer has understood what they've done wrong and positively taken on board the recommendations I've made. I actually came across this while doing a code review for a team that I had not worked with before.

[supercat9]

Thomas Weller wrote:

NEVER ever throw an exception to code a foreseeable condition - even if it might be rare.

I guess it depends what you mean by 'foreseeable'. Certainly if one could readily determine before performing an operation that it would throw an exception that one was planning on catching, and if there was any significant likelihood of such exception occurring, doing an early test before attempting the operation would be a good idea. Testing the length test on the array, for example, would seem appropriate, though in some applications that may be just about the only exception that could be guaranteed not to occur. On the other hand, it may not be possible to determine in advance all exceptions that might occur. In the code sample given, the '.Value' property could throw an exception (e.g. ObjectDisposed or whatever) even if the length of the array was valid. While a general 'Catch' would be icky, there are times when such a thing is appropriate. For example, in expression-evaluation window, nearly all exceptions thrown during expression evaluation should be caught. An application shouldn't die just because someone typed in an expression that caused an exception the application programmer hadn't foreseen. I don't particularly like -1 as a return value, but the overall style would seem appropriate for some applications.

[supercat9]

You'd just have to test the length/count of that thing, whatever it is.. And you have to test all four items to ensure they're not null, and you'd have to somehow know in advance whether any attempt to read .Value might throw an exception of its own (I know properties aren't supposed to throw exceptions, but that doesn't mean they never will).

[Lost User]

Why would there be nulls in there? Well I suppose there could be nulls there, but then I'd still test for null rather than just die and later fix it with a catch..

[supercat9]

harold aptroot wrote:

Well I suppose there could be nulls there, but then I'd still test for null rather than just die and later fix it with a catch.

There are all sorts of things that theoretically could go wrong, especially if the object supports inheritance. Checking in advance for all possible exceptions is frequently infeasible at best, and in many situations impossible (since even if the present implementation of a method can't throw an exception, a future override might). If no condition which would cause an exception is expected, such preemptive coding is often a waste of time (both programmer time and execution time). As for catching an exception and returning an error code versus letting the caller handle it, the latter approach is usually better but not always. If one's objective is to store the output of a function when it works, or -1 if it doesn't, which is nicer:

StoreValue(theFunction()) ' Coded to return -1 in case of failure

or

Dim Result as Double
Try
Result = theFunction()
Catch
Result = -1
End Try
StoreValue(Result)

I would consider the former approach to be much nicer.

[Thomas Weller 0]

supercat9 wrote:

On the other hand, it may not be possible to determine in advance all exceptions that might occur.

Of course not. In that case we wouldn't need exceptions at all... What I mean is: 'Foreseeable' in terms of business/application logic. If something totally unexpected happens (like e.g. the 'ObjectDisposed' you mentioned), there should be a general top level exception handler at the application level, but for sure such an exception must never be swallowed silently by the executing code. Not in a million years, in no circumstance whatsoever!

supercat9 wrote:

I don't particularly like -1 as a return value

Same with me, but in the case of my example -1 has a clear, discrete meaning that can de documented (less than 4 items -> computation not possible), while in the original snippet -1 means sth. went wrong (and I will never tell you what the problem was...). That's a huge difference - especially on large business-scale software projects, where you might have hundreds of such properties... Regards Thomas

www.thomas-weller.de Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.
Programmer - an organism that turns coffee into software.