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Paul Riley wrote:
Wouldn't you say that trying to set something to null that shouldn't ever be null is an exceptional circumstance?
Have you come across the two pronged plugs that plug into the wall only one way? One prong of the plug is keyed and so is the wall receptacle so that the prong must match the wall receptacle's orientation - this is done to prevent something from being plugged in backwards.
The person that designed the plug expected that someone would eventually try to put the plug into the receptacle the wrong way and took measures to ensure the chances of that happening are much smaller than if he did not design the plug with that possibility in mind. My point is that the plug's designer knew that this could be a problem and wants to prevent the device that's being plugged in from working when the plug is put in the wrong way - this is obviously an expected condition.
I view this scenario the same way - since it is possible to set a property to null and the class requires a non-null value - this is nothing exceptional.
Paul Riley wrote:
Why would you do that if one already exists that meets the criteria you're looking for?
Simply becasue the idea of the .NET Platofrm is to provide a space where all activities occur in a managed, type-safe environment. The System namespace is called "system" becuase it exposes classes that you can use to interact with the "system". If your applicaiton throws an exception, throw an applicaiton-specific exception that's derived from System.ApplicationException to avoid confusion with CLR-generated exceptions.
Moreover, CLR-based exceptions usually need to be dealt with in another way than do application-specific exceptions. For example, if the CLR throws an OutOfMemoryException, you'll have to deal with that differnetly than if an application throws it's own memory-specific exception. In the application's case, the problem could be the result of some fixed capacity buffer becomming full whereas the CLR-based exception obviously indicates a problem that affects the entire system.
Given that the System.ApplicationException class is a derivitave of System.Exception, a catch block that catches a System.Exception type will also catch System.ApplicationException exceptions, thus reducing the chance that an applicaiton-specific exception could be missed.
Erik Westermann
Author, Learn XML In A Weekend (October 2002)
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Erik Westermann wrote:
Have you come across the two pronged plugs that plug into the wall only one way? One prong of the plug is keyed and so is the wall receptacle so that the prong must match the wall receptacle's orientation - this is done to prevent something from being plugged in backwards.
Thank god I've been electrocuted enough times in the US to have the faintest idea what you're talking about... our plugs here in the UK are a sensible three-prong design (one vertical, two horizontal) and there's no way on earth anyone's plugging that in the wrong way around! 
Erik Westermann wrote:
The person that designed the plug expected that someone would eventually try to put the plug into the receptacle the wrong way and took measures to ensure the chances of that happening are much smaller than if he did not design the plug with that possibility in mind.
I would argue that this is exactly what the programmer is trying to do in this example. Someone, eventually, is going to pass null to that property and is not going to call IsValid().
Thus the class designer has to check IsValid all over his own class before doing anything with that property and may still have to throw an exception if this causes a situation that is unacceptable. Not only is this inefficient but it's harder for the app programmer to debug.
Erik Westermann wrote:
this is nothing exceptional
I think to a point this is where our opinions part. You are taking "Exception" in the context of "This is an exception to the rule", I think an "Exception" is better described in the context of the program saying "I take exception to this scenario".
Erik Westermann wrote:
Simply becasue the idea of the .NET Platofrm is to provide a space where all activities occur in a managed, type-safe environment. The System namespace is called "system" becuase it exposes classes that you can use to interact with the "system".
If that were true, why are the fundamental base classes all set in the System namespace? Wouldn't Object and Exception be better placed in a "Core" namespace?
However, I do see an argument (although you never quite said this, I think it was your point) that ArgumentNullException is derived from System.SystemException and if someone is trying to catch system-based problems, they will also catch a program defined ArgumentNullException.
That could be a problem, but I would suggest that trying to catch SystemExceptions like this is a problem in and of itself.
For example, RegistryKey.DeleteSubKeyTree will throw an ArgumentNullException if you pass null instead of a string. To argue that this is a system-level exception is ridiculous, just because the registry is part of the system, it must be an application error that caused the problem.
Paul
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Paul Riley wrote:
I think an "Exception" is better described in the context of the program saying "I take exception to this scenario".
It really depends on what you're designing and what its purpose will be. I'm speaking in the snese of who the immediate user is of course. For example, if you're building a class library, you'll probably end up throwing exceptions since you may have no other means of reporting an error or the best way to handle the error is to let the code that called the code in the class library handle the error.
If you're building an applicaiton or a component that an end user will use then it is probably not a good idea to throw an exception since most typical end users don't know what to do when something 'wierd' happens.
Paul Riley wrote:
Wouldn't Object and Exception be better placed in a "Core" namespace?
That was Microsoft's choice.
Paul Riley wrote:
To argue that this is a system-level exception is ridiculous
It is a system-level exception, System.ArgumentNullException is a derivative of System.SystemException. The naming standard appears to focus on the source of the exception, not the entity that casued it.
Erik Westermann
Author, Learn XML In A Weekend (October 2002)
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Erik Westermann wrote:
It really depends on what you're designing and what its purpose will be. I'm speaking in the snese of who the immediate user is of course. For example, if you're building a class library, you'll probably end up throwing exceptions since you may have no other means of reporting an error or the best way to handle the error is to let the code that called the code in the class library handle the error.
I'd agree with you on both a class and an applicaton. Applications should avoid using Exceptions, though I admit I've been guilty of throwing an exception because I'm in the middle of a try block and want to act the same in the event of this error as I would if it were an exception.
That was, however, an ApplicationException.
I wouldn't agree with you in the case of a component - I don't see how this is different from a class library.
Erik Westermann wrote:
That was Microsoft's choice.
Sure, but it does show a total disregard for the selection of the namespace name "System". I feel you're taking that name a lot more seriously than those who designed it.
Erik Westermann wrote:
It is a system-level exception, System.ArgumentNullException is a derivative of System.SystemException. The naming standard appears to focus on the source of the exception, not the entity that casued it.
Except that an ArgumentNullException is NEVER going to be a result of a system problem, it's ALWAYS going to be a result of erroneous programming.
Thus, trying to catch system problems specifically simply by using catch (System.SystemException ex) is already a dangerous idea.
As Martin has pointed out, what if (for some reason I can't think of right now) you wanted to catch all exceptions caused by null arguments? Is it not unfair to expect people to catch the standard ArgumentNullException plus your ArgumentNullException plus my ArgumentNullException, etc, etc?
Paul
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Now I have used exceptions instead of events, and will make no further comment 
Bottom line, you use it where u need it
Paul Riley wrote:
Is it not unfair to expect people to catch the standard ArgumentNullException plus your ArgumentNullException plus my ArgumentNullException, etc, etc?
Say what ? So you say its OK to expect ppl to check for 3 exceptions instead of one, although they check for the same thing? PUDATE: Me dyslexic mind didnt read that right.
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leppie wrote:
Now I have used exceptions instead of events, and will make no further comment
Now that is shoddy coding
leppie wrote:
Say what ? So you say its OK to expect ppl to check for 3 exceptions instead of one, although they check for the same thing? PUDATE: Me dyslexic mind didnt read that right.
 But that's exactly what Erik is suggesting, on the grounds that otherwise anyone trying to catch system-level exceptions will accidentally catch your ArgumentNullexception.
Paul
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Paul Riley wrote:
Now that is shoddy coding
Not if you use it correctly. For example, to abort a thread at a precise point and raise an "event".
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leppie wrote:
Not if you use it correctly. For example, to abort a thread at a precise point and raise an "event".
It still sounds like a dodgy idea. What if something else in the try block throws an exception for another reason? I suppose it's possible to make sure that doesn't happen.
I assume you're trying to kick out of a loop? Isn't there a better way, like "break"?
Just thinking aloud. It strikes me that there should be a way to do this without using an exception, but maybe not. (tell me to stop being nosey, if you want  )
Paul
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Paul Riley wrote:
I assume you're trying to kick out of a loop? Isn't there a better way, like "break"?
Probably, but I needed to send some arguements with the "event", and this was the quickest thing that came to mind. The nice thing is I didnt have to implement an event or had to add/remove a handler. Only a try/catch, for when (if) it happens.
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Fair enough.
Let me put it this way: I used to work with COBOL and some of the worst code I've ever seen was as a direct result of people trying at all costs to avoid using GO TO.
I mean okay, I understand why GO TO is considered tacky but in COBOL at times it can be absolutely necessary because there aren't any other construct-breakers.
So I do accept that sometimes what may be considered tacky is actually the neatest thing to do.
I will say this though: don't avoid implementing events. Once you've done two or three, you get used to them and you can knock them together in a couple of minutes. I love events
Paul
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OK, I do agree, events are the nicer way, but if a tree falls in the forest when nobody's there to hear it, will it make a sound? The was just to test some thing quick(and dirty). I dont I will every let people see such a thing.
Paul Riley wrote:
Once you've done two or three, you get used to them and you can knock them together in a couple of minutes.
Unfortunately, most people can do events, but have no idea what is happening under the hood. Once you understand delegates though, things do become very clear and easy.
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leppie wrote:
OK, I do agree, events are the nicer way, but if a tree falls in the forest when nobody's there to hear it, will it make a sound?
Yes.
leppie wrote:
Unfortunately, most people can do events, but have no idea what is happening under the hood. Once you understand delegates though, things do become very clear and easy.
Absolutely true. It's one thing to copy it out of a book as I did with my first event, it's something else entirely to figure out what a delegate is and use it properly.
It really is a surprisingly simple concept when you get your head around it though (surprising because it took me hours to understand it but then when I did I wondered why it took me so long).
Paul
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Paul Riley wrote:
Yes.
Actually its "No".
bool ProveTreeQuestion(PersonsInForest persons)
{
foreach (Person person in persons)
{
if (person.Hear()) return true;
}
return false;
}
Now if persons.Count = 0, the result will allways be false.
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Erik Westermann wrote:
Simply becasue the idea of the .NET Platofrm is to provide a space where all activities occur in a managed, type-safe environment. The System namespace is called "system" becuase it exposes classes that you can use to interact with the "system". If your applicaiton throws an exception, throw an applicaiton-specific exception that's derived from System.ApplicationException to avoid confusion with CLR-generated exceptions.
But wouldn't this be a problem in itself? Let's say you write a program, that uses class libraries from two or three different vendors and each throws a different kind of exception if the exact same condition (an argument is set to null for example) is met? Wouldn't this be a bad design, too? And why is it more exceptional if you pass an invalid "null" argument to a clr function than to a function of a third party library? I see the point with the out of memory exception - that sure is some kind of "system exception". But ArgumentNullException and ArgumentOutOfRange exception? Actually I never thought about these problems (Visual C# step by step at least uses these two exceptions in user code) - only wether it is the right exception to be thrown from a set accessor.
Cheers
and thanks for your answers
Martin
"Situation normal - all fu***d up"
Illuminatus!
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Martin Häsemeyer wrote:
Wouldn't this be a bad design, too?
How so? You know the exact nature of the problem based on the exception's type. Besides, all exceptions are derivatives of System.Exception; as a result, if you code your catch blocks properly, you'll be able to handle errors from both libraries in this scenario.
Martin Häsemeyer wrote:
And why is it more exceptional if you pass an invalid "null" argument to a clr function than to a function of a third party library?
It isn't. It depands on what the class' designer is atembpting to achieve. An exception is designed to, ultimately, halt your code if it is allowed to 'bubble up' through to the system regardless of what type of exception gets thrown. Exceptons are non-local control structures that let you centralize error handling in one part of your application as opposed to having you sprinkle if statements throughout your code. In some cases; however, it is more approprate a number of cases to use a less computationally expensive means of handling an error.
Erik Westermann
Author, Learn XML In A Weekend (October 2002)
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"An exception is the violation of a programmatic interface's implicit assumptions"
Jeffrey Richter, Applied Microsoft .NET Framework Programming.
He goes on to detail that he believes exceptions should be used for more than just "rare" occurances.
Jared
jparsons@jparsons.org
www.prism.gatech.edu/~gte477n
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Erik Westermann wrote:
Exceptions are for exceptional conditions - conditions that are unexpected during normal circumstances. Exceptions are relatively expensive and aren't that great for stuff like this.
I was just watching the latest .Net show off MSDN and it is all about performance. One of the things they where saying is Exceptions are only expensive if you acctually throw the exception. This makes them very good for doing this sort of thing.
Stephen.
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I want to lighten/darken the shade of a given color. I just wondered if there was a better way, than just adding/substracting an amout from each RGB value, because it in some cases, the difference in color is minute.
 Email: theeclypse@hotmail.com URL: http://www.onyeyiri.co.uk
"All programmers are playwrights and all computers are lousy actors."
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I would have lighten/darken in the HSV color space instead, then come back to RGB, since the V value is exactly the brightness component.
Algorithm here http://www.cs.bham.ac.uk/~mer/colour/hsv.html[^]
MS quote (http://www.microsoft.com/ddk) : As of September 30, 2002, the Microsoft® Windows® 2000 DDK, the Microsoft Windows 98 DDK, and the Microsoft Windows NT® 4.0 DDK will no longer be available for purchase or download on this site. Support for development will ship at the same time as the Windows XP Service Pack 1 (SP1) release.
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void RGBtoHSL(COLORREF rgb, double *H, double *S, double *L)
{
double delta;
double r = (double)GetRValue(rgb)/255;
double g = (double)GetGValue(rgb)/255;
double b = (double)GetBValue(rgb)/255;
double cmax = max(r,max(g,b));
double cmin = min(r,min(g,b));
*L=(cmax+cmin)/2.0;
if(cmax==cmin) {
*S = 0;
*H = 0;
} else {
if(*L < 0.5)
*S = (cmax-cmin)/(cmax+cmin);
else
*S = (cmax-cmin)/(2.0-cmax-cmin);
delta = cmax - cmin;
if(r==cmax)
*H = (g-b)/delta;
else if(g==cmax)
*H = 2.0 +(b-r)/delta;
else
*H=4.0+(r-g)/delta;
*H /= 6.0;
if(*H < 0.0)
*H += 1;
}
}
int HuetoRGB(double m1, double m2, double h)
{
if( h < 0 ) h += 1.0;
if( h > 1 ) h -= 1.0;
if( 6.0*h < 1 )
return ((int) (255 * (m1+(m2-m1)*h*6.0)));
if( 2.0*h < 1 )
return ((int) (255 * m2));
if( 3.0*h < 2.0 )
return ((int) (255 * (m1+(m2-m1)*((2.0/3.0)-h)*6.0)));
return ((int) (255 * m1));
}
void HLStoRGB(double H, double L, double S, int *r, int *g, int *b)
{
double m1, m2;
if(S==0) {
*r = *g = *b = (int) (255 * L);
} else {
if(L <=0.5)
m2 = L*(1.0+S);
else
m2 = L+S-L*S;
m1 = 2.0*L-m2;
*r = HuetoRGB(m1,m2,H+1.0/3.0);
*g = HuetoRGB(m1,m2,H);
*b = HuetoRGB(m1,m2,H-1.0/3.0);
}
}
MS quote (http://www.microsoft.com/ddk) : As of September 30, 2002, the Microsoft® Windows® 2000 DDK, the Microsoft Windows 98 DDK, and the Microsoft Windows NT® 4.0 DDK will no longer be available for purchase or download on this site. Support for development will ship at the same time as the Windows XP Service Pack 1 (SP1) release.
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How about ControlPaint's Light and Dark methods?
James
"And we are all men; apart from the females." - Colin Davies
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Hi everybody,
I wanna know whether I can use System.Windows.Forms namespace in a Web application or not?and if yes,how?
Thanks,
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