Related
As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance.
Closed 10 years ago.
Okay, we know that the following two lines are equivalent -
(0 == i)
(i == 0)
Also, the first method was encouraged in the past because that would have allowed the compiler to give an error message if you accidentally used '=' instead of '=='.
My question is - in today's generation of pretty slick IDE's and intelligent compilers, do you still recommend the first method?
In particular, this question popped into my mind when I saw the following code -
if(DialogResult.OK == MessageBox.Show("Message")) ...
In my opinion, I would never recommend the above. Any second opinions?
I prefer the second one, (i == 0), because it feel much more natural when reading it. You ask people, "Are you 21 or older?", not, "Is 21 less than or equal to your age?"
It doesn't matter in C# if you put the variable first or last, because assignments don't evaluate to a bool (or something castable to bool) so the compiler catches any errors like "if (i = 0) EntireCompanyData.Delete()"
So, in the C# world at least, its a matter of style rather than desperation. And putting the variable last is unnatural to english speakers. Therefore, for more readable code, variable first.
If you have a list of ifs that can't be represented well by a switch (because of a language limitation, maybe), then I'd rather see:
if (InterstingValue1 == foo) { } else
if (InterstingValue2 == foo) { } else
if (InterstingValue3 == foo) { }
because it allows you to quickly see which are the important values you need to check.
In particular, in Java I find it useful to do:
if ("SomeValue".equals(someString)) {
}
because someString may be null, and in this way you'll never get a NullPointerException. The same applies if you are comparing constants that you know will never be null against objects that may be null.
(0 == i)
I will always pick this one. It is true that most compilers today do not allow the assigment of a variable in a conditional statement, but the truth is that some do. In programming for the web today, I have to use myriad of langauges on a system. By using 0 == i, I always know that the conditional statement will be correct, and I am not relying on the compiler/interpreter to catch my mistake for me. Now if I have to jump from C# to C++, or JavaScript I know that I am not going to have to track down assignment errors in conditional statements in my code. For something this small and to have it save that amount of time, it's a no brainer.
I used to be convinced that the more readable option (i == 0) was the better way to go with.
Then we had a production bug slip through (not mine thankfully), where the problem was a ($var = SOME_CONSTANT) type bug. Clients started getting email that was meant for other clients. Sensitive type data as well.
You can argue that Q/A should have caught it, but they didn't, that's a different story.
Since that day I've always pushed for the (0 == i) version. It basically removes the problem. It feels unnatural, so you pay attention, so you don't make the mistake. There's simply no way to get it wrong here.
It's also a lot easier to catch that someone didn't reverse the if statement in a code review than it is that someone accidentally assigned a value in an if. If the format is part of the coding standards, people look for it. People don't typically debug code during code reviews, and the eye seems to scan over a (i = 0) vs an (i == 0).
I'm also a much bigger fan of the java "Constant String".equals(dynamicString), no null pointer exceptions is a good thing.
You know, I always use the if (i == 0) format of the conditional and my reason for doing this is that I write most of my code in C# (which would flag the other one anyway) and I do a test-first approach to my development and my tests would generally catch this mistake anyhow.
I've worked in shops where they tried to enforce the 0==i format but I found it awkward to write, awkward to remember and it simply ended up being fodder for the code reviewers who were looking for low-hanging fruit.
Actually, the DialogResult example is a place where I WOULD recommend that style. It places the important part of the if() toward the left were it can be seen. If it's is on the right and the MessageBox have more parameters (which is likely), you might have to scroll right to see it.
OTOH, I never saw much use in the "(0 == i) " style. If you could remember to put the constant first, you can remember to use two equals signs,
I'm trying always use 1st case (0==i), and this saved my life a few times!
I think it's just a matter of style. And it does help with accidentally using assignment operator.
I absolutely wouldn't ask the programmer to grow up though.
I prefer (i == 0), but I still sort of make a "rule" for myself to do (0 == i), and then break it every time.
"Eh?", you think.
Well, if I'm making a concious decision to put an lvalue on the left, then I'm paying enough attention to what I'm typing to notice if I type "=" for "==". I hope. In C/C++ I generally use -Wall for my own code, which generates a warning on gcc for most "=" for "==" errors anyway. I don't recall seeing that warning recently, perhaps because the longer I program the more reflexively paranoid I am about errors I've made before...
if(DialogResult.OK == MessageBox.Show("Message"))
seems misguided to me. The point of the trick is to avoid accidentally assigning to something.
But who is to say whether DialogResult.OK is more, or less likely to evaluate to an assignable type than MessageBox.Show("Message")? In Java a method call can't possibly be assignable, whereas a field might not be final. So if you're worried about typing = for ==, it should actually be the other way around in Java for this example. In C++ either, neither or both could be assignable.
(0==i) is only useful because you know for absolute certain that a numeric literal is never assignable, whereas i just might be.
When both sides of your comparison are assignable you can't protect yourself from accidental assignment in this way, and that goes for when you don't know which is assignable without looking it up. There's no magic trick that says "if you put them the counter-intuitive way around, you'll be safe". Although I suppose it draws attention to the issue, in the same way as my "always break the rule" rule.
I use (i == 0) for the simple reason that it reads better. It makes a very smooth flow in my head. When you read through the code back to yourself for debugging or other purposes, it simply flows like reading a book and just makes more sense.
My company has just dropped the requirement to do if (0 == i) from its coding standards. I can see how it makes a lot of sense but in practice it just seems backwards. It is a bit of a shame that by default a C compiler probably won't give you a warning about if (i = 0).
Third option - disallow assignment inside conditionals entirely:
In high reliability situations, you are not allowed (without good explanation in the comments preceeding) to assign a variable in a conditional statement - it eliminates this question entirely because you either turn it off at the compiler or with LINT and only under very controlled situations are you allowed to use it.
Keep in mind that generally the same code is generated whether the assignment occurs inside the conditional or outside - it's simply a shortcut to reduce the number of lines of code. There are always exceptions to the rule, but it never has to be in the conditional - you can always write your way out of that if you need to.
So another option is merely to disallow such statements, and where needed use the comments to turn off the LINT checking for this common error.
-Adam
I'd say that (i == 0) would sound more natural if you attempted to phrase a line in plain (and ambiguous) english. It really depends on the coding style of the programmer or the standards they are required to adhere to though.
Personally I don't like (1) and always do (2), however that reverses for readability when dealing with dialog boxes and other methods that can be extra long. It doesn't look bad how it is not, but if you expand out the MessageBox to it's full length. You have to scroll all the way right to figure out what kind of result you are returning.
So while I agree with your assertions of the simplistic comparison of value types, I don't necessarily think it should be the rule for things like message boxes.
both are equal, though i would prefer the 0==i variant slightly.
when comparing strings, it is more error-prone to compare "MyString".equals(getDynamicString())
since, getDynamicString() might return null.
to be more conststent, write 0==i
Well, it depends on the language and the compiler in question. Context is everything.
In Java and C#, the "assignment instead of comparison" typo ends up with invalid code apart from the very rare situation where you're comparing two Boolean values.
I can understand why one might want to use the "safe" form in C/C++ - but frankly, most C/C++ compilers will warn you if you make the typo anyway. If you're using a compiler which doesn't, you should ask yourself why :)
The second form (variable then constant) is more readable in my view - so anywhere that it's definitely not going to cause a problem, I use it.
Rule 0 for all coding standards should be "write code that can be read easily by another human." For that reason I go with (most-rapidly-changing value) test-against (less-rapidly-changing-value, or constant), i.e "i == 0" in this case.
Even where this technique is useful, the rule should be "avoid putting an lvalue on the left of the comparison", rather than the "always put any constant on the left", which is how it's usually interpreted - for example, there is nothing to be gained from writing
if (DateClass.SATURDAY == dateObject.getDayOfWeek())
if getDayOfWeek() is returning a constant (and therefore not an lvalue) anyway!
I'm lucky (in this respect, at least) in that these days in that I'm mostly coding in Java and, as has been mentioned, if (someInt = 0) won't compile.
The caveat about comparing two booleans is a bit of a red-herring, as most of the time you're either comparing two boolean variables (in which case swapping them round doesn't help) or testing whether a flag is set, and woe-betide-you if I catch you comparing anything explicitly with true or false in your conditionals! Grrrr!
In C, yes, but you should already have turned on all warnings and be compiling warning-free, and many C compilers will help you avoid the problem.
I rarely see much benefit from a readability POV.
Code readability is one of the most important things for code larger than a few hundred lines, and definitely i == 0 reads much easier than the reverse
Maybe not an answer to your question.
I try to use === (checking for identical) instead of equality. This way no type conversion is done and it forces the programmer do make sure the right type is passed,
You are right that placing the important component first helps readability, as readers tend to browse the left column primarily, and putting important information there helps ensure it will be noticed.
However, never talk down to a co-worker, and implying that would be your action even in jest will not get you high marks here.
I always go with the second method. In C#, writing
if (i = 0) {
}
results in a compiler error (cannot convert int to bool) anyway, so that you could make a mistake is not actually an issue. If you test a bool, the compiler is still issuing a warning and you shouldn't compare a bool to true or false. Now you know why.
I personally prefer the use of variable-operand-value format in part because I have been using it so long that it feels "natural" and in part because it seems to the predominate convention. There are some languages that make use of assignment statements such as the following:
:1 -> x
So in the context of those languages it can become quite confusing to see the following even if it is valid:
:if(1=x)
So that is something to consider as well. I do agree with the message box response being one scenario where using a value-operand-variable format works better from a readability stand point, but if you are looking for constancy then you should forgo its use.
This is one of my biggest pet peeves. There is no reason to decrease code readability (if (0 == i), what? how can the value of 0 change?) to catch something that any C compiler written in the last twenty years can catch automatically.
Yes, I know, most C and C++ compilers don't turn this on by default. Look up the proper switch to turn it on. There is no excuse for not knowing your tools.
It really gets on my nerves when I see it creeping into other languages (C#,Python) which would normally flag it anyway!
I believe the only factor to ever force one over the other is if the tool chain does not provide warnings to catch assignments in expressions. My preference as a developer is irrelevant. An expression is better served by presenting business logic clearly. If (0 == i) is more suitable than (i == 0) I will choose it. If not I will choose the other.
Many constants in expressions are represented by symbolic names. Some style guides also limit the parts of speech that can be used for identifiers. I use these as a guide to help shape how the expression reads. If the resulting expression reads loosely like pseudo code then I'm usually satisfied. I just let the expression express itself and If I'm wrong it'll usually get caught in a peer review.
We might go on and on about how good our IDEs have gotten, but I'm still shocked by the number of people who turn the warning levels on their IDE down.
Hence, for me, it's always better to ask people to use (0 == i), as you never know, which programmer is doing what.
It's better to be "safe than sorry"
if(DialogResult.OK == MessageBox.Show("Message")) ...
I would always recommend writing the comparison this way. If the result of MessageBox.Show("Message") can possibly be null, then you risk a NPE/NRE if the comparison is the other way around.
Mathematical and logical operations aren't reflexive in a world that includes NULLs.
This question already has answers here:
What is the difference between if(CONST==variable) or if(variable==CONST)?
(5 answers)
Closed 9 years ago.
I've come across some code that flips how a condition is checked and was wondering why this would be done aside from a weird personal quirk. I've never seen any text books use it nor have I seen any sample code done this way.
// why do it this way?
if (5 == myValue)
{
// do something
}
// instead of:
if (myValue == 5)
{
// do something
}
I've only seen this way for == operand but not for any other operands.
Some people like doing that because if you mess up and type a single-equals instead of a double-equals, "if (val = 5)" is only a compiler warning, while "if (5 = val)" is an error (you can't assign to a constant).
I think it's sort of ugly, personally, and that you should be checking your warnings just as much as your errors, but that is the reason for that convention (which is thankfully not universal, but is at least moderately widespread. It is also true that it might not universally have been treated as even a warning by much older compilers, and this convention has been around for a long time.)
Fun fact: I was just reading Code Complete (Second Edition), and Steve McConnell agrees with me, stating his personal preference is "to use number-line ordering and let the compiler warn me about unintended assignments". Steve McConnell by definition knows what he's talking about.
Some folks do it for readability when myValue is deemed less interesting than 5; it puts the constant value in a more prominent place. There is no practical reason for it - purely a judgment call on the part of the coder.
This question already has answers here:
What is the difference between these (bCondition == NULL) and (NULL==bCondition)? [duplicate]
(6 answers)
Closed 9 years ago.
I have received code from someone working earlier on it, and it contains a lot of lines like
while(false==find && false == err && k<kmax)
if(true==refract(ep1,ep2,n1,RI_blood, RI_collagen))
and my favorite line is
if(false == (ret_s<0))
The other code is done really well, documented just fine, but these lines with these odd conditions are throwing me off, and I wonder why they are done that way.
Especially that false==(ret_s<0) is completely confusing, and you kind of need to read that line like three times to understand what they want there.
Is this a common programming style, don't I understand the reasoning for that, or is that just bad style?
Edit: I don't feel this is similar to if(object==NULL) vs if(NULL==object), since this isn't about accidental assigning but about obfuscated if clauses...
Is this a common programming style?
No.
don't I understand the reasoning for that?
Some people like to explicitly compare booleans with true or false, even though the result is exactly the same boolean value. The logic is presumably that, by making the code harder to read and more surprising, people will think harder about it and make fewer assumptions about its behaviour. Or perhaps just that code should be hard to maintain, since it was hard to write.
Others like to write comparisons with constants backwards, which prevents mistakes like if (x = 5) when you meant if (x == 5). Any modern compiler will warn you about this mistake, so again its only real purpose is to make the code harder to read.
Combining these two behaviours gives the bizarre code you posted.
Or is that just bad style?
It's a style. I'm no judge of style, but if you like to keep maintainence programmers on their toes, it certainly does that. Personally, I like my code to be readable, but that's just me.
my favorite line is
I once encountered return a && !b implemented in about ten lines of code. The first line was switch(a).
Yoda Conditions
Using if(constant == variable) instead of if(variable == constant), like if(4 == foo). Because it's like saying "if blue is the sky" or "if tall is the man".
Its a safe guard against assignment in C++.
In C++ it is perfectly legal to do this
if (foo = true) ....
In this case the single = is an assignment and would replace the value of foo.
This is not legal and will generate a compiler error
if (true = foo) ....
Constants and literals are often put on the left because it prevents accidental assignments. Consider typing:
if(foo == bar)
as:
if(foo = bar)
The second might appear to work... but silently clobber foo. If foo is a constant, this error is not longer possible.
It's a self-protection technique that prevents you from accidentally typing an assignment operator (=) instead of equality operator (==), which can introduce strange bugs. Putting the constant value on the left hand side will introduce a compiler error, while putting a variable on the LHS will just silently compile.
Perhaps the original programmer thought that explicit comparison to true or false was clearler than if(condition) or if(!condition) and coded things in that way. I haven't seen this particular style before however.
It's quite subjective but I find while(!find && !err && k<kmax) easier to read.
The code could have been written for a shop where there is a site standard that every conditional statement must include a comparison operator, in order to avoid accidentally leaving out part of the comparison. (Maybe that's a stretch, but you did say that the rest of the code was very good.) That, coupled with a standard or habit of putting the constant on the left to avoid accidentally using = instead of == would give pretty much the code you showed. It doesn't explain the use of 'false' instead of the more natural 'true', though. Maybe it's a (misguided on multiple levels) attempt to gain microefficiency by comparing to zero instead of 1 at the machine level.
for my is only bad style,
if(false == (ret_s<0))
is equals to in C#
if(!(ret_s<0))
What is the difference between (x == "x") and ("x" == x) comparison in C++? Let's say x is a std::string. Is there any reason why one would be preferred over the other?
One is a string literal "X", and the other is an instance of std::string. Some advocate having the constant "x" on the left hand side, because that way you would get a compiler error if you use assignment = instead of equality ==:
if ("x" = x) // Error! Trying to assign to const char[]
if (x = "x") // Setting the value of x to be "x", and evaluating "x".
// Probably not what you want.
Other than that, there's really no difference.
I think both calls will result in call to bool std::string operator==(const std::string&, const std::string&).
This is because there are no implicit conversion operators from std::string to const char*, but there is implicit constructor from const char* to std::string.
EDIT:
on g++ 4.4.5 both comparisons works.
Here says the now closed question on Yoda Conditionals:
This is one of the things that I hate
most when I see it in someone else's
code. I know what it means and why
some people do it this way ("what if I
accidentally put '=' instead?"). For
me it's very much like when a child
goes down the stairs counting the
steps out loud.
Anyway, here are my arguments against
it:
It disrupts the natural flow of reading the program code. We, humans,
say "if value is zero" and not "if
zero is value".
Modern compilers warn you when you have an assignment in your condition,
or actually if your condition consists
of just that assignment, which, yes,
looks suspicious anyway
You shouldn't forget to put double '=' when you are comparing values if
you are a programmer. You may as well
forget to put "!" when testing
non-equality.
-mojuba
Accepted answer:
Ah, yes, "Yoda conditionals" ("If zero
the value is, execute this code you
must!"). I always point anyone who
claims they're "better" at tools like
lint(1). This particular problem has
been solved since the late 70s. Most
modern languages won't even compile
this, as they refuse to coerce the
result of the assignment to a boolean.
As others have said, it certainly
isn't a problem, but it does provoke a
bit of cognitive dissonance.
-TMN
I prefer using for NSStrings...
([x isEqualToString:#"x"])
or for c strings
strcmp(str1,str2);
There is no difference between those two conditions, other than maybe something internal. It's like holding two things in your hands, one in each hand, and comparing them - and then basing then factoring in which hand each one is in. ...That's not something that's a factor.
I just saw this block of code on the Wikipedia article on conditional operators:
Vehicle new_vehicle = arg == 'B' ? bus :
arg == 'A' ? airplane :
arg == 'T' ? train :
arg == 'C' ? car :
arg == 'H' ? horse :
feet;
I've changed the code a little, but the idea is the same. Would you find this use of the conditional operator acceptable? It's much more concise than the if-else construct, and using a switch would definitely open up a whole new set of opportunities for bugs (fall-throughs anyone?). Also, if-elses and switch can't be used as R-values, so you'd have to create the variable first, initialize it and then assign as necessary.
I for one really like this, but I'm wondering what others think.
But the formatting is essential.
EDIT: I still like this. But I understand those who say "the switch statement was made for this". OK, maybe so. But what if the conditions are function calls that return bool? Or a million other things you can't switch on.
Are you switch lovers really trying to convince me that a huge if-else chain is better? Yes, programmers who don't know how to use the conditional operator will not understand this. They should learn how to use it. It's not arcane.
I have used this type of construction many times. As long as it's formatted nicely (i.e. not all on one line, making it unreadable), I don't see a problem with it.
I would use a switch, because this is the kind of thing it was designed for. Yes, there is a risk of fall-through bugs, but this nested-conditional block has a much higher risk of being misunderstood by other programmers.
This is a great example of conditional operator use. I use it in this manner all the time in C++, Java, and Perl.
Not only is there nothing wrong with it, it communicates the intent of the operation in the most concise and clear way possible.
Replacing with if else, or switch construction requires that the snippet
"new_vehicle = "
be repeated in every instance, which requires that the reader read every repeating instance of it to ensure that it is in fact the same in every instance..
I like it. It is similar to an if-else-if ladder, only more concise.
There's a lot of whitespace around the character constants that makes it a bit hard to read. I'd parenthesize the comparisons: (and maybe move the last value in line.)
Vehicle new_vehicle = (arg == 'B') ? bus :
(arg == 'A') ? airplane :
(arg == 'T') ? train :
(arg == 'C') ? car :
(arg == 'H') ? horse :
feet;
Now it looks great.
The conditional operator version is clean, simple, and it's immediately obvious to anybody who knows C or C++ what is happening. Its other virtue is that it returns a value immediately, which means it can be put in the initialization (like this example is).
A switch statement would be more clumsy. It would require that the variable be declared and then initialized, usually a bad idea if it can be avoided. It would take more typing, and would have more places for bugs to creep in. It wouldn't be as clear, since it would be necessary to look at each case to see that it said something like new_vehicle = foo; break;.
If you're going to do this look up here only, then having the conditional version right there is good, as it immediately shows what's happening. If it's going to occur more than once, consider putting it in a function, so that there's only one place to update if anything changes (such as, say, 'R' for carriage or 'L' for helicopter).
Purely a stylistic choice. For small data sets like you present here, then as long as your programming team isn't thrown by such a thing, then its fine in my book.
A switch is both clearer and possibly much more efficient. If I saw code like this at a code review, I'd be worried. Also, this is "the conditional operator" - it is an instance (albeit currently the only one in C and C++) of a ternary operator.
Vehicle new_vehicle = getVehicleByType(arg);
Vehicle getVehicleByType(char arg){
if (arg == 'B') return bus;
if (arg == 'A') return airplane;
if (arg == 'C') return car;
if (arg == 'T') return train;
if (arg == 'H') return horse;
return feet;
}
I like this better. The nested conditional is clever, but I think this is almost as concise and less likely to confuse a future reader. Sorry if the syntax is off, I'm not doing much C nowadays.
EDIT: Fixed return type omission noted in comments. thx!
EDIT: I'm not horrified at your version by the way. I did not exclaim WTF or OMG when i saw it. I just prefer mine a little more :)
I don't particularly care for it.
It doesn't really buy anything, or make anything more clear, and it's a pretty non-standard usage of the operator.
It seems the primary advantage is that it's somewhat clever. I avoid clever unless there's a pretty good (external) reason to be clever.
I would lean toward a switch statement because the compiler will catch duplicate cases. Arguably, this is not an issue in this example but if the list gets really long and is worked on by several different people it is easy to add a duplicate and not realize it.
Read the C++ section of the Wikipedia article a bit more carefully. It explicitly lists some situations where using the ?: operator is the only option, and can't be replaced by if/else or switch.
On the other hand, I wouldn't use it only because it looks prettier.
I've never seen anything written like this before. While it is clever and well-formatted, this seems like the perfect opportunity to use a dictionary/hashtable (assuming Vehicle is an enumeration, which is unclear).
A few people have already mentioned the possibility of using an std::map or other associative array type to do the job. As long as you're only doing this is one place (or a few places), you might consider just using a normal array or vector instead:
Vehicle vehicles[CHAR_MAX];
// Initialization
std::fill_n(vehicles, CHAR_MAX, feet);
vehicles['A'] = airplane;
vehicles['B'] = bus;
vehicles['C'] = car;
vehicles['H'] = horse;
vehicles['T'] = train;
// Use
Vehicle new_vehicle = vehicles[arg];
Depending on how may tables you need/use (that store the same type of object), and the size of the contained objects (Vehicle in this case), this can be a perfectly reasonable alternative to an std::map. If you're creating a lot of tables, or each object is really big, std::map becomes a more reasonable alternative.
When you use an std::map (or unordered_map, etc.) you're using more code to save on data storage. This does the reverse -- but as long as Vehicle is small (say, 4 bytes), one table like the above will typically occupy something like half a kilobyte. It's hard to guess exactly how large the code for std::map is going to be for a specific compiler, but it seems likely that it'll usually be larger than half a kilobyte, so if you're only creating one table like this, std::map may be a net loss.
Of course, if you know that you're only dealing with letters as input, you could reduce the table size quite a bit:
template <class T>
class letter_table {
static const int range = 'Z' - 'A';
T table[range];
public:
// ...
T operator[](int index) {
index -= 'A';
assert(index<range);
return table[index];
}
};
In the example case, this would give a table around 100 bytes -- you can create a pretty fair number of 100-byte tables in the space std::map will normally occupy.
Purely practical:
Plus: The ternary sequence is more flexible, and can be used to avoid the limitations of switch, you could use other operators (e.g. <=, >=) or any other tests, including e.g. string comparisons.
x = IsEven(arg) ? 0 :
(arg < 0) ? -1 : 1; // or whatever
Also, if the switch is a performance bottleneck and you have uneven probabilities, you can force the likeliest tests being done first (due to the not evaluated guarantee for the path not chosen).
So-So
Unlike a switch statement, order is important (unless you stick to ==). That can be an advantage, but being otherwise similar to switch that might be misleading when the maintainer is unfamiliar with the concept or in a hurry.
Many developers may shy away because they aren't sure about the details (which terms will be evaluated, is the rpecedence of the operators ok?) - However, if your developer pool won't grasp a well-presented example, you might have problems that can't be solved by banning ternary operators.
Minus
It isn't as common as switch, thus the optimizer might not treat it the same. Optimizers are know to select the best fit implementation for a switch (table, binary search, comparison sequence, or any combination of this). Optimizers can't reaarange wevaluaiton order, and are less likely to support a table lookup here.
Requires good formatting to be easily recognizable (lining up the '?' and ':') - Sucks when you use tabs.
Aesthetics
I like it for its precision and succinctness, close to mathematical notations. However, that might as well be used against it. It's probably an eyebrow raiser at code reviews, because it is less common and more brittle.
Just for comparison, in C++0x you can have an expression without using the conditional operator or an out-of-line function:
Vehicle new_vehicle = [&]() -> Vehicle {
if (arg == 'B') return bus;
if (arg == 'A') return airplane;
if (arg == 'T') return train;
if (arg == 'C') return car;
if (arg == 'H') return horse;
return feet;
}();
Not really any better, though.
How about:
enum Vehicle { bus = 'B', airplane = 'A', train, car = 'C', horse = 'H', feet = 'F' };
...
new_vehicle = arg;
:-), by the way.
I think its useful for someone who code it, but will be difficult to understand for the reviwer,
"KEEP IT SIMPLE BUDDY"
In my opinion what you've done is acceptable due to the simplicity of the example. If you were doing more things with each case this type of construct could rapidly get messy. For that reason I would prefer a switch or even nested if then elses (if there aren't too many cases), formatted as follows:
if (A) {
//Do A stuff
}
else if (B) {
//Do B stuff
}
else if (C) {
//Do C stuff
}
else {
//Do default stuff
}
It's about the readability of the code, which lends itself to the maintainability of the code. I've never been a huge fan fan of the conditional operator, because I don't like to see multiple expressions on a single line. Conditional operators can be difficult to follow when single stepping the code in a debugger. The simpler the code the easier it is to concentrate on what the code is doing.
Many of us are used to the Iif-functions in various reporting tools or the If-function in Excel where we basically need to use the less clear Iif(arg="B";"Bus";Iif(arg="A";Airplane;"Feet")). I love your sample compared to that :)
I personally would've used if-elses, but I would not have a problem with your sample.