Zero-choice alternative

Lutoslaw

Found in my own code:

if (action == InvalidContentActions.Remove || action == InvalidContentActions.Remove) {

...

Greetings - Gajatko Portable.NET is part of DotGNU, a project to build a complete Free Software replacement for .NET - a system that truly belongs to the developers.

PIEBALDconsult

More like a second chance. Yesterday I somehow wound up writing if ( x != x )..., I enjoyed the warning I got: warning CS1718: Comparison made to same variable; did you mean to compare something else?

supercat9

If action is volatile, it would be possible for the second test to succeed even if the first fails. Indeed, if it's a memory-mapped mapped register, such behavior might even be expected.

Tony Pottier

You could actually write something like that to show the dangers of unsafe multithreading :p

Chris Meech

There should be more code like your example. I'm all for double checking things instead of just single checking. ;P

Chris Meech I am Canadian. [heard in a local bar] In theory there is no difference between theory and practice. In practice there is. [Yogi Berra]

TommyTomToms

I agree. In this day and age you can never be sure of anything...

        DoesJessicaAlbaLoveMe uncertain = new DoesJessicaAlbaLoveMe();
        string yahhhoooooo = "";
        
        if (DoesJessicaAlbaLoveMe != null && DoesJessicaAlbaLoveMe!= null)
        {
            yahhhoooooo = uncertain.ToString().ToString().ToString();
        }
        else
        {
            yahoo = "She's just teasin :P";
        }

A dogged, arrogant belief in self and the childlike idealism that comes with not knowing my limits. This is my greatest blessing, my priceless attribute.

Lutoslaw

TommyTomToms wrote:

DoesJessicaAlbaLoveMe != null && DoesJessicaAlbaLoveMe!= null

It is quite dangerous: if uncertain is volatile, it may change in the meantime. Indeed, if it's not on paper, such behavior might even be expected.

Greetings - Gajatko Portable.NET is part of DotGNU, a project to build a complete Free Software replacement for .NET - a system that truly belongs to the developers.

ClementsDan

I've seriously used code like that to check for NaN.

ClementsDan

Some code I encountered yesterday included:

if (string.IsNullOrEmpty(client) || string.IsNullOrEmpty(client))

I think it's just a typo.

Lutoslaw

ClementsDan wrote:

I think it's just a typo.

In my case the code should be:

if (action == InvalidContentActions.Remove || action == InvalidContentActions.CommentOut)

Greetings - Gajatko Portable.NET is part of DotGNU, a project to build a complete Free Software replacement for .NET - a system that truly belongs to the developers.

supercat9

I've seriously used code like that to check for NaN. If A and B are both floating-point NaN's related to the same condition, what are the values of the six relational operators? If they all report false, then one could test if two numbers were both equal or both NaN with "if (!(a != b))"; if NaN's report not equal to each other but neither greater- nor less-than each other, then maybe "if (!(a > b) && !(a < b))". Of course, unless such statements are commented people would likely find them confusing.

Thomas Weller 0

Not totally sure about that without checking, but: Isn't an if statement atomic, at least such a simple one? I.E.: Is uncertain allowed to change at all between the two boolean checks, may it be volatile or not?

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.

Thomas Weller 0

That's true. But in that case it has to be made explicit in the code, either by using comments or a critical section or whatever may be appropriate. Otherwise it would indeed be a very severe coding horror (since it could cause an error that would be very hard to find...) X| .

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.

Lutoslaw

uncertain = uncertian

I'm affraid that Jessica could change a volatile value of the uncertian even during the '=' symbol.

Greetings - Gajatko Portable.NET is part of DotGNU, a project to build a complete Free Software replacement for .NET - a system that truly belongs to the developers.

supercat9

If "foo" is volatile, the statement "if (foo == foo) bar();" must read the value of foo exactly twice and compare the two values read. If "foo" happens to be an address in normal RAM, the two reads would be most likely read the same data unless an interrupt or task switch happened to occur between them (not terribly likely). Not everything in a processor-based system is RAM, however. When a typical flash memory chip is performing a write cycle, consecutive read operations are guaranteed to return different data. If the generated code for the above 'if' statement didn't read 'foo' twice, the 'if' test would succeed even while the flash was still being written.

Thomas Weller 0

So there's absolutely nothing you can do - this code IS dangerous and stays dangerous :). -- Or is it Jessica who is dangerous... ;)

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.

Thomas Weller 0

Thanks for that - wasn't totally sure about it from the top of my head...

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.

cpkilekofp

No, an if statement is not guaranteed to be atomic as it can be decomposed into multiple binary instructions, and a task switch can occur between any of those instructions unless the compiler designates the entire sequence as a critical section.

Bram Fokke

Wouldn't float.IsNaN(x) be a more readable way to achieve that?

KarstenK

That is a good test for a custom "!=" operator X|

Greetings from Germany