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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.
I am a quite new programmer, and I sometimes have really dumb questions,
In a few weeks I am supposed to give back this big semester project and I would have liked a bit of help for my optimization.
Somewhere I needed to get a Quantitiy (class derived from a double) and strip it down to a just a number without integers and print it in a window (I dont have the slightest clue how the latter works, it was given to us by the teacher, but it's not the problem here).
And so I created two variables to do so, which gave me something like this:
int lil_patate=q_nutriments;
string patate(to_string(lil_patate));
And I would have like to set that in a single line, writing that;
string patate(to_string(int lil_patate=q_nutriments));
which of course doesnt work, as I expected, but I would have loved a bit of help to get something working that would be simpler than the first version but doing the same thing,
Thanks for the help and have a nice day :)
Humphrey
If you need to be able to reference lil_patate elsewhere in your code then you can't make this factorisation at all. If you don't need to refer to lil_patate elsewhere then get rid of it and initialise patate directly from q_nutrients:
string patate(to_string(q_nutriments));
However, while this may improve the readability of the code, it doesn't represent an optimisation in any technical sense.
it's a pretty common practice that constants are prefixed with k (e.g. k_pi). But what does the k mean?
Is it simply that c already meant char?
It's a historical oddity, still common practice among teams who like to blindly apply coding standards that they don't understand.
Long ago, most commercial programming languages were weakly typed; automatic type checking, which we take for granted now, was still mostly an academic topic. This meant that is was easy to write code with category errors; it would compile and run, but go wrong in ways that were hard to diagnose. To reduce these errors, a chap called Simonyi suggested that you begin each variable name with a tag to indicate its (conceptual) type, making it easier to spot when they were misused. Since he was Hungarian, the practise became known as "Hungarian notation".
Some time later, as typed languages (particularly C) became more popular, some idiots heard that this was a good idea, but didn't understand its purpose. They proposed adding redundant tags to each variable, to indicate its declared type. The only use for them is to make it easier to check the type of a variable; unless someone has changed the type and forgotten to update the tag, in which case they are actively harmful.
The second (useless) form was easier to describe and enforce, so it was blindly adopted by many, many teams; decades later, you still see it used, and even advocated, from time to time.
"c" was the tag for type "char", so it couldn't also be used for "const"; so "k" was chosen, since that's the first letter of "konstant" in German, and is widely used for constants in mathematics.
I haven't seen it that much, but maybe it comes from certain languages' (the germanic ones in particular) spelling of the word constant - konstant.
Don't use Hungarian Notation. If you want constants to stand out, make them all caps.
As a side note: there are a lot of things in the Google Coding Standards that are poor practice (in terms of code readability). That is what happens when you design a coding standard by committee.
It means the value is k-onstant.
I think mathematical convention was the precedent. k is used in maths all the time as just some constant.
K stands for konstant, a wordplay on constant. It relates to Coding Styles.
It's just a matter of preference, some people and projects use them which means they also embrace the Hungarian notation, many don't. That's not that important.
If you're unsure what a prefix or style might mean, always check if the project has a coding style reference and read that.
Actually, whenever I define constants in typescript, I do something like this -
NODE_ENV = 'production';
But recently, I saw that the k prefix is being used in the Flutter SDK. It makes sense to me to keep using the k prefix cuz' it helps your editor/IDE in searching out constants in your codebase.
It's a convention, probably from math. But there are other suggestions for constant too, for example Kernighan and Ritchie in their book "The C language" suggest writing constants' name in capital letters (e.g. #define MAX 55).
I think, it means coefficient (as k in math means)
This question is inspired by this question, which features the following code snippet.
int s;
if((s = foo()) == ERROR)
print_error();
I find this style hard to read and prone to error (as the original question demonstrates -- it was prompted by missing parentheses around the assignment). I would instead write the following, which is actually shorter in terms of characters.
int s = foo();
if(s == ERROR)
print_error();
This is not the first time I've seen this idiom though, and I'm guessing there are reasons (perhaps historical) for it being so often used. What are those reasons?
I think it's for hysterical reasons, that early compilers were not so smart at optimizing. By putting it on one line as a single expression, it gives the compiler a hint that the same value fetched from foo() can be tested rather than specifically loading the value from s.
I prefer the clarity of your second example, with the assignment and test done later. A modern compiler will have no trouble optimizing this into registers, avoiding unnecessary loads from memory store.
When you are writing a loop, it is sometimes desirable to use the first form, as in this famous example from K&R:
int c;
while ((c = getchar()) != EOF) {
/* stuff */
}
There is no elegant "second-form" way of writing this without a repetition:
int c = getchar();
while (c != EOF) {
/* stuff */
c = getchar();
}
Or:
int c;
for (c = getchar(); c != EOF; c = getchar()) {
/* stuff */
}
Now that the assignment to c is repeated, the code is more error-prone, because one has to keep both the statements in sync.
So one has to be able to learn to read and write the first form easily. And given that, it seems logical to use the same form in if conditions as well.
I tend to use the first form mostly because I find it easy to read—as someone else said, it couples the function call and the return value test much more closely.
I make a conscious attempt at combining the two whenever possible. The "penalty" in size isn't enough to overcome the advantage in clarity, IMO.
The advantage in clarity comes from one fact: for a function like this, you should always think of calling the function and testing the return value as a single action that cannot be broken into two parts ("atomic", if you will). You should never call such a function without immediately testing its return value.
Separating the two (at all) leads to a much greater likelihood that you'll sometimes skip checking the return value completely. Other times, you'll accidentally insert some code between the call and the test of the return value that actually depends on that function having succeeded. If you always combine it all into a single statement, it (nearly) eliminates any possibility of falling into these traps.
I would always go for the second. It's easier to read, there's no danger of omitting the parentheses around the assignment and it is easier to step through with a debugger.
I often find the separation of the assignment out into a different line makes debugger watch or "locals" windows behave better vis-a-vis the presence and correct value of "s", at least in non-optimized builds.
It also allows the use of step-over separately on the assignment and test lines (again, in non-optimized builds), which can be helpful if you don't want to go mucking around in disassembly or mixed view.
YMMV per compiler and debugger and for optimized builds, of course.
I personally prefer for assignments and tests to be on different lines. It is less syntactically complicated, less error prone, and more easily understood. It also allows the compiler to give you more precise error/warning locations and often makes debugging easier.
It also allows me to more easily do things like:
int rc = function();
DEBUG_PRINT(rc);
if (rc == ERROR) {
recover_from_error();
} else {
keep_on_going(rc);
}
I prefer this style so much that in the case of loops I would rather:
while (1) {
int rc = function();
if (rc == ERROR) {
break;
}
keep_on_going(rc);
}
than do the assignment in the while conditional. I really don't like for my tests to have side-effects.
I often prefer the first form. I couldn't say exactly why, but it has something to do with the semantic involved.
The second style feels to me more like 2 separate operations. Call the function and then do something with the result, 2 different things. In the first style it's one logical unit. Call the function, save the temprary result and eventually handle the error case.
I know it's pretty vague and far from being completely rational, so I will use one or the other depending on the importance of the saved variable or the test case.
I believe that clarity should always prime over optimizations or "simplifications" based only on the amount of characters typed. This belief has stopped me from making many silly mistakes.
Separating the assignement and the comparison makes both clearer and so less error-prone, even if the duplication of the comparison might introduce a mistake once in a while. Among other things, parentheses become quickly hard to distinguish and keeping everything on one line introduces more parentheses. Also, splitting it up limits statements to doing only one of either fetching a value or assigning one.
However, if you expect people who will read your code to be more comfortable using the one-line idiom, then it is wide-spread enough not to cause any problems for most programmers. C programmers will definately be aware of it, even those that might find it awkward.
Myself and a colleague have a dispute about which of the following is more elegant. I won't say who's who, so it is impartial. Which is more elegant?
public function set hitZone(target:DisplayObject):void
{
if(_hitZone != target)
{
_hitZone.removeEventListener(MouseEvent.ROLL_OVER, onBtOver);
_hitZone.removeEventListener(MouseEvent.ROLL_OUT, onBtOut);
_hitZone.removeEventListener(MouseEvent.MOUSE_DOWN, onBtDown);
_hitZone = target;
_hitZone.addEventListener(MouseEvent.ROLL_OVER, onBtOver, false, 0, true);
_hitZone.addEventListener(MouseEvent.ROLL_OUT, onBtOut, false, 0, true);
_hitZone.addEventListener(MouseEvent.MOUSE_DOWN, onBtDown, false, 0, true);
}
}
...or...
public function set hitZone(target:DisplayObject):void
{
if(_hitZone == target)return;
_hitZone.removeEventListener(MouseEvent.ROLL_OVER, onBtOver);
_hitZone.removeEventListener(MouseEvent.ROLL_OUT, onBtOut);
_hitZone.removeEventListener(MouseEvent.MOUSE_DOWN, onBtDown);
_hitZone = target;
_hitZone.addEventListener(MouseEvent.ROLL_OVER, onBtOver, false, 0, true);
_hitZone.addEventListener(MouseEvent.ROLL_OUT, onBtOut, false, 0, true);
_hitZone.addEventListener(MouseEvent.MOUSE_DOWN, onBtDown, false, 0, true);
}
In most cases, returning early reduces the complexity and makes the code more readable.
It's also one of the techniques applied in Spartan programming:
Minimal use of Control
Minimizing the use of conditionals by using specialized
constructs such ternarization,
inheritance, and classes such as Class
Defaults, Class Once and Class
Separator
Simplifying conditionals with early return.
Minimizing the use of looping constructs, by using action applicator
classes such as Class Separate and
Class FileSystemVisitor.
Simplifying logic of iteration with early exits (via return,
continue and break statements).
In your example, I would choose option 2, as it makes the code more readable. I use the same technique when checking function parameters.
This is one of those cases where it's ok to break the rules (i.e. best practices). In general you want to have as few return points in a function as possible. The practical reason for this is that it simplifies your reading of the code, since you can just always assume that each and every function will take its arguments, do its logic, and return its result. Putting in extra returns for various cases tends to complicate the logic and increase the amount of time necessary to read and fully grok the code. Once your code reaches the maintenance stage then multiple returns can have a huge impact on the productivity of new programmers as they try to decipher the logic (its especially bad when comments are sparse and the code unclear). The problem grows exponentially with respect to the length of the function.
So then why in this case does everyone prefer option 2? It's because you're are setting up a contract that the function enforces through validating incoming data, or other invariants that might need to be checked. The prettiest syntax for constructing the validation is the check each condition, returning immediately if the condition fails validity. That way you don't have to maintain some kind of isValid boolean through all of your checks.
To sum things up: we're really looking at how to write validation code and not general logic; option 2 is better for validation code.
As long as the early returns are organized as a block at the top of the function/method body, then I think they're much more readable than adding another layer of nesting.
I try to avoid early returns in the middle of the body. Sometimes they're the best way, but most of the time I think they complicate.
Also, as a general rule I try to minimize nesting control structures. Obviously you can take this one too far, so you have to use some discretion. Converting nested if's to a single switch/case is much clearer to me, even if the predicates repeat some sub-expressions (and assuming this isn't a performance critical loop in a language too dumb to do subexpression elimination). Particularly I dislike the combination of nested ifs in long function/method bodies, since if you jump into the middle of the code for some reason you end up scrolling up and down to mentally reconstruct the context of a given line.
In my experience, the issue with using early returns in a project is that if others on the project aren't used to them, they won't look for them. So early returns or not - if there are multiple programmers involved, make sure everyone's at least aware of their presence.
I personally write code to return as soon as it can, as delaying a return often introduces extra complexity eg trying to safely exit a bunch of nested loops and conditions.
So when I look at an unfamiliar function, the very first thing I do is look for all the returns. What really helps there is to set up your syntax colouring to give return a different colour from anything else. (I go for red.) That way, the returns become a useful tool for determining what the function does, rather than hidden stumbling blocks for the unwary.
Ah the guardian.
Imho, yes - the logic of it is clearer because the return is explicit and right next to the condition, and it can be nicely grouped with similar structures. This is even more applicable where "return" is replaced with "throw new Exception".
As said before, early return is more readable, specially if the body of a function is long, you may find that deleting a } by mistake in a 3 page function (wich in itself is not very elegant) and trying to compile it can take several minutes of non-automatable debugging.
It also makes the code more declarative, because that's the way you would describe it to another human, so probably a developer is close enough to one to understand it.
If the complexity of the function increases later, and you have good tests, you can simply wrap each alternative in a new function, and call them in case branches, that way you mantain the declarative style.
In this case (one test, no else clause) I like the test-and-return. It makes it clear that in that case, there's nothing to do, without having to read the rest of the function.
However, this is splitting the finest of hairs. I'm sure you must have bigger issues to worry about :)
option 2 is more readable, but the manageability of the code fails when a else may be required to be added.
So if you are sure, there is no else go for option 2, but if there could be scope for an else condition then i would prefer option 1
Option 1 is better, because you should have a minimal number of return points in procedure.
There are exceptions like
if (a) {
return x;
}
return y;
because of the way a language works, but in general it's better to have as few exit points as it is feasible.
I prefer to avoid an immediate return at the beginning of a function, and whenever possible put the qualifying logic to prevent entry to the method prior to it being called. Of course, this varies depending on the purpose of the method.
However, I do not mind returning in the middle of the method, provided the method is short and readable. In the event that the method is large, in my opinion, it is already not very readable, so it will either be refactored into multiple functions with inline returns, or I will explicitly break from the control structure with a single return at the end.
I am tempted to close it as exact duplicate, as I saw some similar threads already, including Invert “if” statement to reduce nesting which has good answers.
I will let it live for now... ^_^
To make that an answer, I am a believer that early return as guard clause is better than deeply nested ifs.
I have seen both types of codes and I prefer first one as it is looks easily readable and understandable for me but I have read many places that early exist is the better way to go.
There's at least one other alternative. Separate the details of the actual work from the decision about whether to perform the work. Something like the following:
public function setHitZone(target:DisplayObject):void
{
if(_hitZone != target)
setHitZoneUnconditionally(target);
}
public function setHitZoneUnconditionally(target:DisplayObject):void
{
_hitZone.removeEventListener(MouseEvent.ROLL_OVER, onBtOver);
_hitZone.removeEventListener(MouseEvent.ROLL_OUT, onBtOut);
_hitZone.removeEventListener(MouseEvent.MOUSE_DOWN, onBtDown);
_hitZone = target;
_hitZone.addEventListener(MouseEvent.ROLL_OVER, onBtOver, false, 0, true);
_hitZone.addEventListener(MouseEvent.ROLL_OUT, onBtOut, false, 0, true);
_hitZone.addEventListener(MouseEvent.MOUSE_DOWN, onBtDown, false, 0, true);
}
Any of these three (your two plus the third above) are reasonable for cases as small as this. However, it would be A Bad Thing to have a function hundreds of lines long with multiple "bail-out points" sprinkled throughout.
I've had this debate with my own code over the years. I started life favoring one return and slowly have lapsed.
In this case, I prefer option 2 (one return) simply because we're only talking about 7 lines of code wrapped by an if() with no other complexity. It's far more readable and function-like. It flows top to bottom. You know you start at the top and end at the bottom.
That being said, as others have said, if there were more guards at the beginning or more complexity or if the function grows, then I would prefer option 1: return immediately at the beginning for a simple validation.