We Keep Coding

More elegant way to update index into circular list?

I have a list of questions that the user will iterate through, they can start at any question, but they do have a order to them, so in order to do this I just maintain an index into the array and increment it like so:
CurrentQuestion = (++CurrentQuestion < questions.Length) ? CurrentQuestion : 0;
It isn't necessarily obvious what is happening here, is there a more elegant way to do this?

I have a strong aversion to using ++ on a variable and then that variable again in the same statement. I believe this line works fine in C#, but lines like this are undefined in C/C++, and so they raise a flag for me. I would prefer
CurrentQuestion = (CurrentQuestion+1) % questions.Length;
Which I think of as the idiomatic way of doing clock-arithmetic in C-like languages.

It isn't necessarily obvious what is happening here, is there a more elegant way to do this?
While it's not immediately obvious to some, I know exactly what that's doing.
However, what you may want to consider is that it's more important to write readable code than it is to be clever. Code has to be maintained, and you are NOT smarter than the compiler.
Write the code like thus, and be happy with it:
//ensure that the CurrentQuestion counter increments and loops back around after hitting "list max"
CurrentQuestion = CurrentQuestion + 1;
if (CurrentQuestion >= questions.Length) {
CurrentQuestion = 0;
} // meta-comment: use braces incase you have to add more later
The important bit is that this code is now readable, and it's still optimized. It does exactly what the other code does, and we can change parts later without a lot of re-reading of the code.
Also note some semantics I used here.
Always use the braces, even when you don't think you need them.
Do CurrentQuestion = CurrentQuestion + 1; instead of either CurrentQuestion += 1; or CurrentQuestion++; or ++CurrentQuestion; because the first is much more explicit on intent. Always write intentful code.

There's no need for the conditional operator
CurrentQuestion = ++CurrentQuestion % questions.Length;
but I guess which one you prefer is a matter of style more than anything else

I don't like this... Is this cheating the language?

I have seen something like the following a couple times... and I hate it. Is this basically 'cheating' the language? Or.. would you consider this to be 'ok' because the IsNullOrEmpty is evaluated first, all the time?
(We could argue whether or not a string should be NULL when it comes out of a function, but that isn't really the question.)
string someString;
someString = MagicFunction();
if (!string.IsNullOrEmpty(someString) && someString.Length > 3)
{
// normal string, do whatever
}
else
{
// On a NULL string, it drops to here, because first evaluation of IsNullOrEmpty fails
// However, the Length function, if used by itself, would throw an exception.
}
EDIT:
Thanks again to everyone for reminding me of this language fundamental. While I knew "why" it worked, I can't believe I didn't know/remember the name of the concept.
(In case anyone wants any background.. I came upon this while troubleshooting exceptions generated by NULL strings and .Length > x exceptions... in different places of the code. So when I saw the above code, in addition to everything else, my frustration took over from there.)

You're taking advantage of a language feature known as short circuiting. This is not cheating the language but in fact using a feature exactly how it was designed to be used.

If you are asking if its ok to depend on the "short circuit" relational operators && and ||, then yes thats totally fine.

There is nothing wrong with this, as you just want to make certain you won't get a nullpointer exception.
I think it is reasonable to do.
With Extensions you can make it cleaner, but the basic concept would still be valid.

This code is totally valid, but I like to use the Null Coalesce Operator for avoid null type checks.
string someString = MagicFunction() ?? string.Empty;
if (someString.Length > 3)
{
// normal string, do whatever
}
else
{
// NULL strings will be converted to Length = 0 and will end up here.
}

Theres nothing wrong with this.
if(conditions are evaluated from left to right so it's perfectly fine to stack them like this.

This is valid code, in my opinion (although declaring a variable and assigning it on the next line is pretty annoying), but you should probably realize that you can enter the else-block also in the condition where the length of the string is < 3.

That looks to me like a perfectly reasonable use of logical short-circuitting--if anything, it's cheating with the language. I've only recently come from VB6 which didn't ever short-circuit, and that really annoyed me.
One problem to watch out for is that you might need to test for Null again in that else clause, since--as written--you're winding up there with both Null strings and length-less-than-three strings.

This is perfectly valid and there is nothing wrong with using it that way. If you are following documented behaviour for the language than all is well. In C# the syntax you are using are the conditional logic operators and thier docemented bahviour can be found on MSDN
For me it's the same as when you do not use parenthesis for when doing multiplication and addition in the same statement because the language documents that the multiplication operations will get carried out first.

Relying on short-circuiting is the "right thing" to do in most cases. It leads to terser code with fewer moving parts. Which generally means easier to maintain. This is especially true in C and C++.
I would seriously reconsider hiring someone who is not familiar with (and does not know how to use) short-circuiting operations.

I find it OK :) You're just making sure that you don't access a NULL variable.
Actually, I always do such checking before doing any operation on my variable (also, when indexing collections and so) - it's safer, a best practice, that's all ..

It makes sense because C# by default short circuits the conditions, so I think it's fine to use that to your advantage. In VB there may be some issues if the developer uses AND instead of ANDALSO.

I don't think it's any different than something like this:
INT* pNumber = GetAddressOfNumber();
if ((pNUmber != NULL) && (*pNumber > 0))
{
// valid number, do whatever
}
else
{
// On a null pointer, it drops to here, because (pNumber != NULL) fails
// However, (*pNumber > 0), if used by itself, would throw and exception when dereferencing NULL
}
It's just taking advantage of a feature in the language. This kind of idiom has been in common use, I think, since C started executing Boolean expressions in this manner (or whatever language did it first).)

If it were code in c that you compiled into assembly, not only is short-circuiting the right behavior, it's faster. In machine langauge the parts of the if statement are evaluated one after another. Not short-circuiting is slower.

Writing code cost a lot of $ to a company. But maintaining it cost more !
So, I'm OK with your point : chance are that this line of code will not be understood immediatly by the guy who will have to read it and correct it in 2 years.
Of course, he will be asked to correct a critical production bug. He will search here and there and may not notice this.
We should always code for the next guy and he may be less clever that we are. To me, this is the only thing to remember.
And this implies that we use evident language features and avoid the others.
All the best, Sylvain.

A bit off topic but if you rand the same example in vb.net like this
dim someString as string
someString = MagicFunction()
if not string.IsNullOrEmpty(someString) and someString.Length > 3 then
' normal string, do whatever
else
' do someting else
end if
this would go bang on a null (nothing) string but in VB.Net you code it as follows do do the same in C#
dim someString as string
someString = MagicFunction()
if not string.IsNullOrEmpty(someString) andalso someString.Length > 3 then
' normal string, do whatever
else
' do someting else
end if
adding the andalso make it behave the same way, also it reads better. as someone who does both vb and c' development the second vb one show that the login is slighty different and therefor easyer to explain to someone that there is a differeance etc.
Drux

SubSonic RESTHandler Question

I'm playing with the SubSonic RESTHandler for the first time and it's awesome... There is one quirk tho, that I'm curious about.
RESTHandler.cs (line 319):
//if this column is a string, by default do a fuzzy search
if(comp == Comparison.Like || column.IsString)
{
comp = Comparison.Like;
paramValue = String.Concat("%", paramValue, "%");
}
This little blurp of code forces all searches on string columns to wildcard searches by default. This seems counter intutive, since you've provided a nice set of comparisons we can add to a parameter (_is, _notequal, etc...). Is there a reason this was done? The EvalComparison uses "Comparison.Equals" as it's default, so unless a like is explicitly needed the " || column.IsString" looks like it should be removed since it breaks the ability to use different types of comparisons.
This was driving me crazy, since you can't do a "WHERE Field = X" without modifiying code...
Just curious if this is more of a feature than a bug...
Thanks!
Zach

It's because this is a LIKE operation which for a DB usually allows string operations. The feeling at the time was that if you wanted equals you could just use that.
It's been a while since I've touched this code - if you'd be kind enough to open a bug I'll take a look at it.

It does indeed look like a feature. It's based on the idea that, if I am searching for a string in a column without the wildcards, I must match the string exactly or I get no hits. I suspect that this was done to make programming search textboxes easier.

Is this a reasonable use of the ternary operator? [closed]

Closed. This question is opinion-based. It is not currently accepting answers.
Want to improve this question? Update the question so it can be answered with facts and citations by editing this post.
Closed 9 years ago.
Improve this question
Are there any understanding / maintainability issues that result from code like
inVar1 == 0 ? NULL : v.push_back(inVar1);
inVar2 == 0 ? NULL : v.push_back(inVar2);
and so forth.
The possibly confusing idea is using the ternary operator for program flow rather than variable assignment, which is the usual explanation.
I haven't seen coding standards at work that address this usage, so while I'm comfortable doing this I'd like to find out if there is a good reason not to.

I think it's confusing and a lot harder to read than simply typing;
if (inVar != 0)
v.push_back(inVar);
I had to scan your example several times to figure out what the result would be with any certainty. I'd even prefer a single-line if() {} statement than your example - and I hate single-line if statements :)

The ternary operator is meant to return a value.
IMO, it should not mutate state, and the return value should be used.
In the other case, use if statements. If statements are meant to execute code blocs.

The ternary is a good thing, and I generally promote it's usage.
What you're doing here however tarnishes it's credibility. It's shorter, yes, but it's needlessly complicated.

I think this should be avoided. You could use a 1-line if statement in its place.
if(inVar1 != 0) v.push_back(inVar1);

Compilers these days will make an if as fast as a ternary operator.
You goal should be how easy is it for another software developer to read.
I vote for
if ( inVar != 0 )
{
v.push_back( inVar );
}
why the brackets...because one day you may want to put something else in there and the brackets are pre-done for you. Most editors these days will put them in anyway.

Your use of the ternary operator gains you nothing and you hurt the codes readability.
Since the ternary operator returns a value that you are not using it is odd code. The use of an if is much more clear in a case like yours.

As litb mentioned in the comments, this isn't valid C++. GCC, for example, will emit an error on this code:
error: `(&v)->std::vector<_Tp, _Alloc>::push_back [with _Tp = int, _Alloc =
std::allocator<int>](((const int&)((const int*)(&inVar1))))' has type `void'
and is not a throw-expression
However, that can be worked around by casting:
inVar1 == 0 ? (void)0 : v.push_back(inVar1);
inVar2 == 0 ? (void)0 : v.push_back(inVar2);
But at what cost? And for what purpose?
It's not like using the ternary operator here is any more concise than an if-statement in this situation:
inVar1 == 0 ? NULL : v.push_back(inVar1);
if(inVar1 != 0) v.push_back(inVar1);

While, in practice, I agree with the sentiments of those who discourage this type of writing (when reading, you have to do extra work to scan the expression for its side effects), I'd like to offer
!inVar1 ?: v.push_back(inVar1);
!inVar2 ?: v.push_back(inVar2);
...if you're going for obscure, that is. GCC allows x ?: y in place of x ? x : y. :-)

I use ternary operator when I need to call some function with conditional arguments - in this case it is better then if.
Compare:
printf("%s while executing SQL: %s",
is_sql_err() ? "Error" : "Warning", sql_msg());
with
if (is_sql_err())
printf("Error while executing SQL: %s", sql_msg());
else
printf("Warning while executing SQL: %s", sql_msg());
I find the former is more appealing. And it complies to DRY principle, unlike latter - you don't need to write two nearly identical lines.

I think you would be better served in doing a proper if structure. I even prefer to always have braces with my if structures, in the event I have to add lines later to the conditional execution.
if (inVar != 0) {
v.push_back(inVar);
}

I think that sometimes the ternary are a necessary evil in initializer lists for constructors. I use them mostly for constructors where I want to allocate memory and set some pointer to point at it before the body of the constructor.
An example, suppose you had an integer storage class that you wanted to have take a vector as an input but the internal representation is an array:
class foo
{
public:
foo(std::vector<int> input);
private:
int* array;
unsigned int size;
};
foo:foo(std::vector<int> input):size(input.size()), array( (input.size()==0)?
NULL : new int[input.size])
{
//code to copy elements and do other start up goes here
}
This is how I use the ternary operator. I don't think it is as confusing as some people do but I do think that one should limit how much they use it.

Most of the tortured ternaries (how's that for alliteration?) I see are merely attempts at putting logic that really belongs in an if statement in a place where an if statement doesn't belong or can't go.
For instance:
if (inVar1 != 0)
v.push_back(inVar1);
if (inVar2 != 0)
v.push_back(inVar2);
works assuming that v.push_back is void, but what if it's returning a value that needs to get passed to another function? In that case, it would have to look something like this:
SomeType st;
if (inVar1 != 0)
st = v.push_back(inVar1);
else if (inVar2 != 0)
st = v.push_back(inVar2);
SomeFunc(st);
But that's more to digest for such a simple piece of code. My solution: define another function.
SomeType GetST(V v, int inVar1, int inVar2){
if (inVar1 != 0)
return v.push_back(inVar1);
if (inVar2 != 0)
return v.push_back(inVar2);
}
//elsewhere
SomeFunc(GetST(V v, inVar1, inVar2));
At any rate, the point is this: if you have some logic that's too tortured for a ternary but will clutter up your code if it's put in an if statement, put it somewhere else!

inVar1 != 0 || v.push_back(inVar1);
inVar2 != 0 || v.push_back(inVar2);
common pattern found in languages like Perl.

If you have multiple method invocations in one or both of the tenary arguments then its wrong. All lines of code regardless of what statement should be short and simple, ideally not compounded.

A proper if statement is more readable, as others have mentioned. Also, when you're stepping through your code with a debugger, you won't be able to readily see which branch of an if is taken when everything is in one line or you're using a ternary expression:
if (cond) doIt();
cond ? noop() : doIt();
Whereas the following is much nicer to step through (whether you have the braces or not):
if (cond) {
doIt();
}

As mentioned, it's not shorter or clearer than a 1 line if statement. However, it's also no longer - and isn't really that hard to grok. If you know the ternary operator, it's pretty obvious what's happening.
After all, I don't think anyone would have a problem if it was being assigned to a variable (even if it was mutating state as well):
var2 = inVar1 == 0 ? NULL : v.push_back(inVar1);
The fact that the ternary operator always returns a value - IMO - is irrelevant. There's certainly no requirement that you use all return values...after all, an assignment returns a value.
That being said, I'd replace it with an if statement if I ran across it with a NULL branch.
But, if it replaced a 3 line if statement:
if (inVar == 0) {
v.doThingOne(1);
} else {
v.doThingTwo(2);
}
with:
invar1 == 0 ? v.doThingOne(1) : v.doThingTwo(2);
I might leave it...depending on my mood. ;)

Setting a boolean value based on an integer

I found this statement is some old code and it took me a second to figure out...
IsTestActive = (TestStateID == 1 ? true : false);
Please correct me if I'm wrong but isn't this the same as this one?:
IsTestActive = (TestStateID == 1);
If it is, why would you ever want to use the first? Which one is more readable? (I think the latter, but I'd like to see what others think.)

Yes, it is exactly the same.
Yes, the latter is more readable.

IsTestActive = (TestStateID == 1);
is definitely more readable.
You could make a case for defining a constant
ACTIVE = 1
then replacing the boolean variable IsTestActive with
(TestStateID == ACTIVE)
The way the code is now, the state of the boolean IsTestActive will be erroneous if the state of TestStateID changes without updating the boolean. Bypassing the boolean and testing the real source of the information you're after will remove the possibility of this error.

No, there's no practical reason for using the first version, world isn't perfect, and neither are programmers.

Readability depends on where you use this construct. I often find something like
(TestStateID == 1 ? true : false)
more readable.

Well, I don't know about other languages, but in PHP it's even more easy, using type-casting:
$IsTestActive = (boolean)$TestStateId;