Related
Which is better in accessing a property value?
Accessing like this
propertyobjA.objB.Prop1
propertyobjA.objB.Prop2
or assign to var
var objB = propertyobjA.objB;
then call objB.Prop1 and objB.Prop1
Which one improves performance in c#?
To be perfectly the honest, the answer is likely that the second will be faster, but I can pretty much guarantee that it will not matter in the slightest. You should be careful of thinking too hard about optimisation too early. 99% of all performance issues are down to much larger issues such as hitting a database too frequently, etc., not trivial issues like this. Even if there was a tiny difference between the two cases, unless this is some of the most time-critical software on the planet, what matters is readability (not that either are hard to read in this case), not which is faster.
It depends on what objB is. If you are calculating something (which you shouldn't do but can do) then of course assigning it to a value will yield better performance.
Another note, you should avoid having dependencies on sub properties of a variable, since you are putting a higher coupling between the classes.
I think this won't make a big difference performancewise (second alternative might be a bit faster). But this is not the place where your performance problems (if any) come from.
UPDATE: Thinking about, the value of propertyobjA.objB could change between getting Prop1 and Prop2, so the two alternatives cannot be considered as being the same code.
The impact to performance largely depends on the implementation of the propertyObjA.objB property getter. For instance, if it is simply implemented as:
public Foo objB { get { return this._objB; } }
Then calling that twice will have a negligible impact on performance.
If, however, that same property did something computationally expensive, then your second suggestion would perform better.
That being said, the framework guidelines state that you should not use property getters to hide potentially computationally expensive operations, instead preferring a method call instead, e.g.:
public objB ComputeB ();
You really ought to not concern yourself with things like that when writing code in a higher level language such as c#.
Modern compilers of such languages as c# and java are extremely sofisticated and will perform all kinds optimizations on your code. The end result for you as developer is that you will never see a difference in performance when writing a particular trivial piece of code one way or the other. The compiler will pick the most optimal way.
Everything else is down to preference. If you like to chain several property accesses, that's fine. If you like to assign an intermediate result to a variable to improve readability of your code, that's fine too.
When I ran ReSharper on my code, for example:
if (some condition)
{
Some code...
}
ReSharper gave me the above warning (Invert "if" statement to reduce nesting), and suggested the following correction:
if (!some condition) return;
Some code...
I would like to understand why that's better. I always thought that using "return" in the middle of a method problematic, somewhat like "goto".
It is not only aesthetic, but it also reduces the maximum nesting level inside the method. This is generally regarded as a plus because it makes methods easier to understand (and indeed, many static analysis tools provide a measure of this as one of the indicators of code quality).
On the other hand, it also makes your method have multiple exit points, something that another group of people believes is a no-no.
Personally, I agree with ReSharper and the first group (in a language that has exceptions I find it silly to discuss "multiple exit points"; almost anything can throw, so there are numerous potential exit points in all methods).
Regarding performance: both versions should be equivalent (if not at the IL level, then certainly after the jitter is through with the code) in every language. Theoretically this depends on the compiler, but practically any widely used compiler of today is capable of handling much more advanced cases of code optimization than this.
A return in the middle of the method is not necessarily bad. It might be better to return immediately if it makes the intent of the code clearer. For example:
double getPayAmount() {
double result;
if (_isDead) result = deadAmount();
else {
if (_isSeparated) result = separatedAmount();
else {
if (_isRetired) result = retiredAmount();
else result = normalPayAmount();
};
}
return result;
};
In this case, if _isDead is true, we can immediately get out of the method. It might be better to structure it this way instead:
double getPayAmount() {
if (_isDead) return deadAmount();
if (_isSeparated) return separatedAmount();
if (_isRetired) return retiredAmount();
return normalPayAmount();
};
I've picked this code from the refactoring catalog. This specific refactoring is called: Replace Nested Conditional with Guard Clauses.
This is a bit of a religious argument, but I agree with ReSharper that you should prefer less nesting. I believe that this outweighs the negatives of having multiple return paths from a function.
The key reason for having less nesting is to improve code readability and maintainability. Remember that many other developers will need to read your code in the future, and code with less indentation is generally much easier to read.
Preconditions are a great example of where it is okay to return early at the start of the function. Why should the readability of the rest of the function be affected by the presence of a precondition check?
As for the negatives about returning multiple times from a method - debuggers are pretty powerful now, and it's very easy to find out exactly where and when a particular function is returning.
Having multiple returns in a function is not going to affect the maintainance programmer's job.
Poor code readability will.
As others have mentioned, there shouldn't be a performance hit, but there are other considerations. Aside from those valid concerns, this also can open you up to gotchas in some circumstances. Suppose you were dealing with a double instead:
public void myfunction(double exampleParam){
if(exampleParam > 0){
//Body will *not* be executed if Double.IsNan(exampleParam)
}
}
Contrast that with the seemingly equivalent inversion:
public void myfunction(double exampleParam){
if(exampleParam <= 0)
return;
//Body *will* be executed if Double.IsNan(exampleParam)
}
So in certain circumstances what appears to be a a correctly inverted if might not be.
The idea of only returning at the end of a function came back from the days before languages had support for exceptions. It enabled programs to rely on being able to put clean-up code at the end of a method, and then being sure it would be called and some other programmer wouldn't hide a return in the method that caused the cleanup code to be skipped. Skipped cleanup code could result in a memory or resource leak.
However, in a language that supports exceptions, it provides no such guarantees. In a language that supports exceptions, the execution of any statement or expression can cause a control flow that causes the method to end. This means clean-up must be done through using the finally or using keywords.
Anyway, I'm saying I think a lot of people quote the 'only return at the end of a method' guideline without understanding why it was ever a good thing to do, and that reducing nesting to improve readability is probably a better aim.
I'd like to add that there is name for those inverted if's - Guard Clause. I use it whenever I can.
I hate reading code where there is if at the beginning, two screens of code and no else. Just invert if and return. That way nobody will waste time scrolling.
http://c2.com/cgi/wiki?GuardClause
It doesn't only affect aesthetics, but it also prevents code nesting.
It can actually function as a precondition to ensure that your data is valid as well.
This is of course subjective, but I think it strongly improves on two points:
It is now immediately obvious that your function has nothing left to do if condition holds.
It keeps the nesting level down. Nesting hurts readability more than you'd think.
Multiple return points were a problem in C (and to a lesser extent C++) because they forced you to duplicate clean-up code before each of the return points. With garbage collection, the try | finally construct and using blocks, there's really no reason why you should be afraid of them.
Ultimately it comes down to what you and your colleagues find easier to read.
Guard clauses or pre-conditions (as you can probably see) check to see if a certain condition is met and then breaks the flow of the program. They're great for places where you're really only interested in one outcome of an if statement. So rather than say:
if (something) {
// a lot of indented code
}
You reverse the condition and break if that reversed condition is fulfilled
if (!something) return false; // or another value to show your other code the function did not execute
// all the code from before, save a lot of tabs
return is nowhere near as dirty as goto. It allows you to pass a value to show the rest of your code that the function couldn't run.
You'll see the best examples of where this can be applied in nested conditions:
if (something) {
do-something();
if (something-else) {
do-another-thing();
} else {
do-something-else();
}
}
vs:
if (!something) return;
do-something();
if (!something-else) return do-something-else();
do-another-thing();
You'll find few people arguing the first is cleaner but of course, it's completely subjective. Some programmers like to know what conditions something is operating under by indentation, while I'd much rather keep method flow linear.
I won't suggest for one moment that precons will change your life or get you laid but you might find your code just that little bit easier to read.
Performance-wise, there will be no noticeable difference between the two approaches.
But coding is about more than performance. Clarity and maintainability are also very important. And, in cases like this where it doesn't affect performance, it is the only thing that matters.
There are competing schools of thought as to which approach is preferable.
One view is the one others have mentioned: the second approach reduces the nesting level, which improves code clarity. This is natural in an imperative style: when you have nothing left to do, you might as well return early.
Another view, from the perspective of a more functional style, is that a method should have only one exit point. Everything in a functional language is an expression. So if statements must always have an else clauses. Otherwise the if expression wouldn't always have a value. So in the functional style, the first approach is more natural.
There are several good points made here, but multiple return points can be unreadable as well, if the method is very lengthy. That being said, if you're going to use multiple return points just make sure that your method is short, otherwise the readability bonus of multiple return points may be lost.
Performance is in two parts. You have performance when the software is in production, but you also want to have performance while developing and debugging. The last thing a developer wants is to "wait" for something trivial. In the end, compiling this with optimization enabled will result in similar code. So it's good to know these little tricks that pay off in both scenarios.
The case in the question is clear, ReSharper is correct. Rather than nesting if statements, and creating new scope in code, you're setting a clear rule at the start of your method. It increases readability, it will be easier to maintain, and it reduces the amount of rules one has to sift through to find where they want to go.
Personally I prefer only 1 exit point. It's easy to accomplish if you keep your methods short and to the point, and it provides a predictable pattern for the next person who works on your code.
eg.
bool PerformDefaultOperation()
{
bool succeeded = false;
DataStructure defaultParameters;
if ((defaultParameters = this.GetApplicationDefaults()) != null)
{
succeeded = this.DoSomething(defaultParameters);
}
return succeeded;
}
This is also very useful if you just want to check the values of certain local variables within a function before it exits. All you need to do is place a breakpoint on the final return and you are guaranteed to hit it (unless an exception is thrown).
Avoiding multiple exit points can lead to performance gains. I am not sure about C# but in C++ the Named Return Value Optimization (Copy Elision, ISO C++ '03 12.8/15) depends on having a single exit point. This optimization avoids copy constructing your return value (in your specific example it doesn't matter). This could lead to considerable gains in performance in tight loops, as you are saving a constructor and a destructor each time the function is invoked.
But for 99% of the cases saving the additional constructor and destructor calls is not worth the loss of readability nested if blocks introduce (as others have pointed out).
Many good reasons about how the code looks like. But what about results?
Let's take a look to some C# code and its IL compiled form:
using System;
public class Test {
public static void Main(string[] args) {
if (args.Length == 0) return;
if ((args.Length+2)/3 == 5) return;
Console.WriteLine("hey!!!");
}
}
This simple snippet can be compiled. You can open the generated .exe file with ildasm and check what is the result. I won't post all the assembler thing but I'll describe the results.
The generated IL code does the following:
If the first condition is false, jumps to the code where the second is.
If it's true jumps to the last instruction. (Note: the last instruction is a return).
In the second condition the same happens after the result is calculated. Compare and: got to the Console.WriteLine if false or to the end if this is true.
Print the message and return.
So it seems that the code will jump to the end. What if we do a normal if with nested code?
using System;
public class Test {
public static void Main(string[] args) {
if (args.Length != 0 && (args.Length+2)/3 != 5)
{
Console.WriteLine("hey!!!");
}
}
}
The results are quite similar in IL instructions. The difference is that before there were two jumps per condition: if false go to next piece of code, if true go to the end. And now the IL code flows better and has 3 jumps (the compiler optimized this a bit):
First jump: when Length is 0 to a part where the code jumps again (Third jump) to the end.
Second: in the middle of the second condition to avoid one instruction.
Third: if the second condition is false, jump to the end.
Anyway, the program counter will always jump.
In theory, inverting if could lead to better performance if it increases branch prediction hit rate. In practice, I think it is very hard to know exactly how branch prediction will behave, especially after compiling, so I would not do it in my day-to-day development, except if I am writing assembly code.
More on branch prediction here.
That is simply controversial. There is no "agreement among programmers" on the question of early return. It's always subjective, as far as I know.
It's possible to make a performance argument, since it's better to have conditions that are written so they are most often true; it can also be argued that it is clearer. It does, on the other hand, create nested tests.
I don't think you will get a conclusive answer to this question.
There are a lot of insightful answers there already, but still, I would to direct to a slightly different situation: Instead of precondition, that should be put on top of a function indeed, think of a step-by-step initialization, where you have to check for each step to succeed and then continue with the next. In this case, you cannot check everything at the top.
I found my code really unreadable when writing an ASIO host application with Steinberg's ASIOSDK, as I followed the nesting paradigm. It went like eight levels deep, and I cannot see a design flaw there, as mentioned by Andrew Bullock above. Of course, I could have packed some inner code to another function, and then nested the remaining levels there to make it more readable, but this seems rather random to me.
By replacing nesting with guard clauses, I even discovered a misconception of mine regarding a portion of cleanup-code that should have occurred much earlier within the function instead of at the end. With nested branches, I would never have seen that, you could even say they led to my misconception.
So this might be another situation where inverted ifs can contribute to a clearer code.
It's a matter of opinion.
My normal approach would be to avoid single line ifs, and returns in the middle of a method.
You wouldn't want lines like it suggests everywhere in your method but there is something to be said for checking a bunch of assumptions at the top of your method, and only doing your actual work if they all pass.
In my opinion early return is fine if you are just returning void (or some useless return code you're never gonna check) and it might improve readability because you avoid nesting and at the same time you make explicit that your function is done.
If you are actually returning a returnValue - nesting is usually a better way to go cause you return your returnValue just in one place (at the end - duh), and it might make your code more maintainable in a whole lot of cases.
I'm not sure, but I think, that R# tries to avoid far jumps. When You have IF-ELSE, compiler does something like this:
Condition false -> far jump to false_condition_label
true_condition_label:
instruction1
...
instruction_n
false_condition_label:
instruction1
...
instruction_n
end block
If condition is true there is no jump and no rollout L1 cache, but jump to false_condition_label can be very far and processor must rollout his own cache. Synchronising cache is expensive. R# tries replace far jumps into short jumps and in this case there is bigger probability, that all instructions are already in cache.
I think it depends on what you prefer, as mentioned, theres no general agreement afaik.
To reduce annoyment, you may reduce this kind of warning to "Hint"
My idea is that the return "in the middle of a function" shouldn't be so "subjective".
The reason is quite simple, take this code:
function do_something( data ){
if (!is_valid_data( data ))
return false;
do_something_that_take_an_hour( data );
istance = new object_with_very_painful_constructor( data );
if ( istance is not valid ) {
error_message( );
return ;
}
connect_to_database ( );
get_some_other_data( );
return;
}
Maybe the first "return" it's not SO intuitive, but that's really saving.
There are too many "ideas" about clean codes, that simply need more practise to lose their "subjective" bad ideas.
There are several advantages to this sort of coding but for me the big win is, if you can return quick you can improve the speed of your application. IE I know that because of Precondition X that I can return quickly with an error. This gets rid of the error cases first and reduces the complexity of your code. In a lot of cases because the cpu pipeline can be now be cleaner it can stop pipeline crashes or switches. Secondly if you are in a loop, breaking or returning out quickly can save you a lots of cpu. Some programmers use loop invariants to do this sort of quick exit but in this you can broke your cpu pipeline and even create memory seek problem and mean the the cpu needs to load from outside cache. But basically I think you should do what you intended, that is end the loop or function not create a complex code path just to implement some abstract notion of correct code. If the only tool you have is a hammer then everything looks like a nail.
I was reading through some C# code of mine today and found this line:
if (ProgenyList.ItemContainerGenerator.Status != System.Windows.Controls.Primitives.GeneratorStatus.ContainersGenerated) return;
Notice that you can tell without scrolling that it's an "if" statement that works with ItemContainerGenerator.Status, but you can't easily tell that if the "if" clause evaluates to "true" the method will return at that point.
Realistically I should have moved the "return" statement to a line by itself, but it got me thinking about languages that allow the "then" part of the statement first. If C# permitted it, the line could look like this:
return if (ProgenyList.ItemContainerGenerator.Status != System.Windows.Controls.Primitives.GeneratorStatus.ContainersGenerated);
This might be a bit "argumentative", but I'm wondering what people think about this kind of construct. It might serve to make lines like the one above more readable, but it also might be disastrous. Imagine this code:
return 3 if (x > y);
Logically we can only return if x > y, because there's no "else", but part of me looks at that and thinks, "are we still returning if x <= y? If so, what are we returning?"
What do you think of the "then before the if" construct? Does it exist in your language of choice? Do you use it often? Would C# benefit from it?
Let's reformat that a bit and see:
using System.Windows.Controls.Primitives;
...
if (ProgenyList.ItemContainerGenerator.Status != GeneratorStatus.ContainersGenerated)
{
return;
}
Now how hard is it to see the return statement? Admittedly in SO you still need to scroll over to see the whole of the condition, but in an IDE you wouldn't have to... partly due to not trying to put the condition and the result on the same line, and party due to the using directive.
The benefit of the existing C# syntax is that the textual order reflects the execution order - if you want to know what will happen, you read the code from top to bottom.
Personally I'm not a fan of "return if..." - I'd rather reformat code for readability than change the ordering.
I don't like the ambiguity this invites. Consider the following code:
doSomething(x)
if (x > y);
doSomethingElse(y);
What is it doing? Yes, the compiler could figure it out, but it would look pretty confusing for a programmer.
Yes.
It reads better. Ruby has this as part of its syntax - the term being 'statement modifiers'
irb(main):001:0> puts "Yay Ruby!" if 2 == 2
Yay Ruby!
=> nil
irb(main):002:0> puts "Yay Ruby!" if 2 == 3
=> nil
To close, I need to stress that you need to 'use this with discretion'. The ruby idiom is to use this for one-liners. It can be abused - however I guess this falls into the realm of responsible development - don't constrain the better developers by building in restrictions to protect the poor ones.
It's look ugly for me. The existing syntax much better.
if (x > y) return 3;
I think it's probably OK if the scope were limited to just return statements. As I said in my comment, imagine if this were allowed:
{
doSomething();
doSomethingElse();
// 50 lines...
lastThink();
} if (a < b);
But even just allowing it only on return statements is probably a slippery slope. People will ask, "return x if (a); is allowed, so why not something like doSomething() if (a);?" and then you're on your way down the slope :)
I know other languages do get away with it, but C#'s philosophy is more about making The One Right WayTM easy and having more than one way to do something is usually avoided (though with exceptions). Personally, I think it works pretty well, because I can look at someone else's code and know that it's pretty much in the same style that I'd write it in.
I don't see any problem with
return 3 if (x > y);
It probably bothers you because you are not accustomed to the syntax. It is also nice to be able to say
return 3 unless y <= x
This is a nice syntax option, but I don't think that c# needs it.
I think Larry Wall was very smart when he put this feature into Perl. The idea is that you want to put the most important part at the beginning where it's easy to see. If you have a short statement (i.e. not a compound statement), you can put it before the if/while/etc. If you have a long (i.e. compound) statement, it goes in braces after the condition.
Personally I like languages that let me choose.
That said, if you refactor as well as reformat, it probably doesn't matter what style you use, because they will be equally readable:
using System.Windows.Controls.Primitives;
...
var isContainersGenerated =
ProgenyList.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated;
if (!isContainersGenerated) return;
//alternatively
return if (!isContainersGenerated);
There is a concern reading the code that you think a statement will execute only later to find out it might execute.
For example if you read "doSomething(x)", you're thinking "okay so this calls doSomething(x)" but then you read the "if" after it and have to realise that the previous call is conditional on the if statement.
When the "if" is first you know immediately that the following code might happen and can treat it as such.
We tend to read sequentially, so reading and going in your mind "the following might happen" is a lot easier than reading and then realising everything you just read needs to be reparsed and that you need to evaluate everything to see if it's within the scope of your new if statement.
Both Perl and Ruby have this and it works fine. Personally I'm fine with as much functionality you want to throw at me. The more choices I have to write my code the better the overall quality, right? "The right tool for the job" and all that.
Realistically though, it's kind of a moot point since it's pretty late for such a fundamental addition in C#'s lifecycle. We're at the point where any minor syntax change would take a lot of work to implement due to the size of the compiler code and its syntax parsing algorithm. For a new addition to be even considered it would have to bring quite a bit of functionality, and this is just a (not so) different way of saying the same thing.
Humans read beginning to end. In analyzing code flow, limits of the short term memory make it more difficult to read postfix conditions due to additional backtracking required. For short expressions, this may not be a problem, but for longer expressions it will incur significant overhead for users that are not seasoned in the language they are reading.
Agreed with confusing , I never heard about this construction before , so I think correct way using then before if must always contents the result of else, like
return (x > y) ? 3 : null;
else way there is no point of using Imperative constructions like
return 3 if (x > y);
return 4 if (x = y);
return 5 if (x < y);
imho It's kinda weird, because I have no idea where to use it...
It's like a lot of things really, it makes perfect sense when you use it in a limited context(a one liner), and makes absolutely no sense if you use it anywhere else.
The problem with that of course is that it'd be almost impossible to restrict the use to where it makes sense, and allowing its use where it doesn't make sense is just odd.
I know that there's a movement coming out of scripting languages to try and minimize the number of lines of code, but when you're talking about a compiled language, readability is really the key and as much as it might offend your sense of style, the 4 line model is clearer than the reversed if.
I think it's a useful construct and a programmer would use it to emphasize what is important in the code and to de-emphasize what is not important. It is about writing intention-revealing code.
I use something like this (in coffeescript):
index = bla.find 'a'
return if index is -1
The most important thing in this code is to get out (return) if nothing is found - notice the words I just used to explain the intention were in the same order as that in the code.
So this construct helps me to code in a way which reflects my intention slightly better.
It shouldn't be too surprising to realize that the order in which correct English or traditional programming-language grammar has typically required, isn't always the most effective or simplest way to create meaning.
Sometimes you need to let everything hang out and truly reassess what is really the best way to do something.
It's considered grammatically incorrect to put the answer before the question, why would it be any different in code?
For quick tasks where I only use an instantiated object once, I am aware that I can do the following:
int FooBarResult = (new Foo()).Bar();
I say this is perfectly acceptable with non-disposable objects and more readable than the alternative:
Foo MyOnceUsedFoo = new Foo();
int FooBarResult = MyOnceUsedFoo.Bar();
Which do you use, and why?
Would you ever use this type of anonymous instantiation in a production app?
Preference: with parenthesis "(new Foo()).Bar();" or without "new Foo().Bar();"?
(Edited to abstract question away from Random class)
Side note regarding random numbers: In fact, no, your specific example (new Random().Next(0,100)) is completely unacceptable. The generated random numbers will be far from uniform.
Other than that, in general, there is not much difference between the two. The compiler will most probably generate the exact same code in either case. You should go with the most readable case (long statements might harm readability; more code will do it too, so you have to make the trade-off in your specific case).
By the way, if you chose to go with the single line case, omit the unnecessary parens (new MyObject().Method() will do).
You might want to consider the implications of using the code in the debugger. The second case will allow you to inspect the object you've created, whereas the first won't. Granted you can always back out to the second case when you're attempting to debug the code.
I've done it both ways and don't really have a preference. I prefer whatever looks more readable, which is highly dependent on the complexity of the class and method being called.
BTW -- you might want to pick a different example. I fear that your point might get lost in discussions over the best way to generate random numbers.
If you are only using the object once, the first way is better all the time.
It is shorter and clearer, because it makes it explicit that you will not use the object later.
It will probably compile to the same CIL anyway, so there's no advantage to the second form.
First statement. It's more readable, has less code and doesn't leave temps around.
The second one is debugging friendly, while the first one isn't. The second wins only because of this.
In fact the first way, creating a temporary, is more readable for two reasons:
1) it's more concise
There's less code to read, there's no unnecessary local variable introduced, and no potential name clash with another local, or shadowing of any variable with the same name in an enclosing scope
2) it communicates something that the second form doesn't, that the object is being used temporarily.
Reading it, I know that that instance is never going to be used again, so in my "mental compiler" that I use to understand the code I'm reading, I don't have to keep a reference to it any more than the code keeps a reference to it.
As Mehrdad notes, though, doing it with a Random class isn't a good idea.
As he also notes, the redundant parentheses make it less concise; unless you're in a dusty corner of a language, assume that competent programmers know the language's operator precedence. In this case, even if I don't know the operator precedence, the alternative parse (calling new on a function's return) is nonsensical, so the "obvious" reading is the correct reading.
int RandomIndex = (new Random()).Next(0,100);
int RandomIndex = new Random().Next(0,100);
When I ran ReSharper on my code, for example:
if (some condition)
{
Some code...
}
ReSharper gave me the above warning (Invert "if" statement to reduce nesting), and suggested the following correction:
if (!some condition) return;
Some code...
I would like to understand why that's better. I always thought that using "return" in the middle of a method problematic, somewhat like "goto".
It is not only aesthetic, but it also reduces the maximum nesting level inside the method. This is generally regarded as a plus because it makes methods easier to understand (and indeed, many static analysis tools provide a measure of this as one of the indicators of code quality).
On the other hand, it also makes your method have multiple exit points, something that another group of people believes is a no-no.
Personally, I agree with ReSharper and the first group (in a language that has exceptions I find it silly to discuss "multiple exit points"; almost anything can throw, so there are numerous potential exit points in all methods).
Regarding performance: both versions should be equivalent (if not at the IL level, then certainly after the jitter is through with the code) in every language. Theoretically this depends on the compiler, but practically any widely used compiler of today is capable of handling much more advanced cases of code optimization than this.
A return in the middle of the method is not necessarily bad. It might be better to return immediately if it makes the intent of the code clearer. For example:
double getPayAmount() {
double result;
if (_isDead) result = deadAmount();
else {
if (_isSeparated) result = separatedAmount();
else {
if (_isRetired) result = retiredAmount();
else result = normalPayAmount();
};
}
return result;
};
In this case, if _isDead is true, we can immediately get out of the method. It might be better to structure it this way instead:
double getPayAmount() {
if (_isDead) return deadAmount();
if (_isSeparated) return separatedAmount();
if (_isRetired) return retiredAmount();
return normalPayAmount();
};
I've picked this code from the refactoring catalog. This specific refactoring is called: Replace Nested Conditional with Guard Clauses.
This is a bit of a religious argument, but I agree with ReSharper that you should prefer less nesting. I believe that this outweighs the negatives of having multiple return paths from a function.
The key reason for having less nesting is to improve code readability and maintainability. Remember that many other developers will need to read your code in the future, and code with less indentation is generally much easier to read.
Preconditions are a great example of where it is okay to return early at the start of the function. Why should the readability of the rest of the function be affected by the presence of a precondition check?
As for the negatives about returning multiple times from a method - debuggers are pretty powerful now, and it's very easy to find out exactly where and when a particular function is returning.
Having multiple returns in a function is not going to affect the maintainance programmer's job.
Poor code readability will.
As others have mentioned, there shouldn't be a performance hit, but there are other considerations. Aside from those valid concerns, this also can open you up to gotchas in some circumstances. Suppose you were dealing with a double instead:
public void myfunction(double exampleParam){
if(exampleParam > 0){
//Body will *not* be executed if Double.IsNan(exampleParam)
}
}
Contrast that with the seemingly equivalent inversion:
public void myfunction(double exampleParam){
if(exampleParam <= 0)
return;
//Body *will* be executed if Double.IsNan(exampleParam)
}
So in certain circumstances what appears to be a a correctly inverted if might not be.
The idea of only returning at the end of a function came back from the days before languages had support for exceptions. It enabled programs to rely on being able to put clean-up code at the end of a method, and then being sure it would be called and some other programmer wouldn't hide a return in the method that caused the cleanup code to be skipped. Skipped cleanup code could result in a memory or resource leak.
However, in a language that supports exceptions, it provides no such guarantees. In a language that supports exceptions, the execution of any statement or expression can cause a control flow that causes the method to end. This means clean-up must be done through using the finally or using keywords.
Anyway, I'm saying I think a lot of people quote the 'only return at the end of a method' guideline without understanding why it was ever a good thing to do, and that reducing nesting to improve readability is probably a better aim.
I'd like to add that there is name for those inverted if's - Guard Clause. I use it whenever I can.
I hate reading code where there is if at the beginning, two screens of code and no else. Just invert if and return. That way nobody will waste time scrolling.
http://c2.com/cgi/wiki?GuardClause
It doesn't only affect aesthetics, but it also prevents code nesting.
It can actually function as a precondition to ensure that your data is valid as well.
This is of course subjective, but I think it strongly improves on two points:
It is now immediately obvious that your function has nothing left to do if condition holds.
It keeps the nesting level down. Nesting hurts readability more than you'd think.
Multiple return points were a problem in C (and to a lesser extent C++) because they forced you to duplicate clean-up code before each of the return points. With garbage collection, the try | finally construct and using blocks, there's really no reason why you should be afraid of them.
Ultimately it comes down to what you and your colleagues find easier to read.
Guard clauses or pre-conditions (as you can probably see) check to see if a certain condition is met and then breaks the flow of the program. They're great for places where you're really only interested in one outcome of an if statement. So rather than say:
if (something) {
// a lot of indented code
}
You reverse the condition and break if that reversed condition is fulfilled
if (!something) return false; // or another value to show your other code the function did not execute
// all the code from before, save a lot of tabs
return is nowhere near as dirty as goto. It allows you to pass a value to show the rest of your code that the function couldn't run.
You'll see the best examples of where this can be applied in nested conditions:
if (something) {
do-something();
if (something-else) {
do-another-thing();
} else {
do-something-else();
}
}
vs:
if (!something) return;
do-something();
if (!something-else) return do-something-else();
do-another-thing();
You'll find few people arguing the first is cleaner but of course, it's completely subjective. Some programmers like to know what conditions something is operating under by indentation, while I'd much rather keep method flow linear.
I won't suggest for one moment that precons will change your life or get you laid but you might find your code just that little bit easier to read.
Performance-wise, there will be no noticeable difference between the two approaches.
But coding is about more than performance. Clarity and maintainability are also very important. And, in cases like this where it doesn't affect performance, it is the only thing that matters.
There are competing schools of thought as to which approach is preferable.
One view is the one others have mentioned: the second approach reduces the nesting level, which improves code clarity. This is natural in an imperative style: when you have nothing left to do, you might as well return early.
Another view, from the perspective of a more functional style, is that a method should have only one exit point. Everything in a functional language is an expression. So if statements must always have an else clauses. Otherwise the if expression wouldn't always have a value. So in the functional style, the first approach is more natural.
There are several good points made here, but multiple return points can be unreadable as well, if the method is very lengthy. That being said, if you're going to use multiple return points just make sure that your method is short, otherwise the readability bonus of multiple return points may be lost.
Performance is in two parts. You have performance when the software is in production, but you also want to have performance while developing and debugging. The last thing a developer wants is to "wait" for something trivial. In the end, compiling this with optimization enabled will result in similar code. So it's good to know these little tricks that pay off in both scenarios.
The case in the question is clear, ReSharper is correct. Rather than nesting if statements, and creating new scope in code, you're setting a clear rule at the start of your method. It increases readability, it will be easier to maintain, and it reduces the amount of rules one has to sift through to find where they want to go.
Personally I prefer only 1 exit point. It's easy to accomplish if you keep your methods short and to the point, and it provides a predictable pattern for the next person who works on your code.
eg.
bool PerformDefaultOperation()
{
bool succeeded = false;
DataStructure defaultParameters;
if ((defaultParameters = this.GetApplicationDefaults()) != null)
{
succeeded = this.DoSomething(defaultParameters);
}
return succeeded;
}
This is also very useful if you just want to check the values of certain local variables within a function before it exits. All you need to do is place a breakpoint on the final return and you are guaranteed to hit it (unless an exception is thrown).
Avoiding multiple exit points can lead to performance gains. I am not sure about C# but in C++ the Named Return Value Optimization (Copy Elision, ISO C++ '03 12.8/15) depends on having a single exit point. This optimization avoids copy constructing your return value (in your specific example it doesn't matter). This could lead to considerable gains in performance in tight loops, as you are saving a constructor and a destructor each time the function is invoked.
But for 99% of the cases saving the additional constructor and destructor calls is not worth the loss of readability nested if blocks introduce (as others have pointed out).
Many good reasons about how the code looks like. But what about results?
Let's take a look to some C# code and its IL compiled form:
using System;
public class Test {
public static void Main(string[] args) {
if (args.Length == 0) return;
if ((args.Length+2)/3 == 5) return;
Console.WriteLine("hey!!!");
}
}
This simple snippet can be compiled. You can open the generated .exe file with ildasm and check what is the result. I won't post all the assembler thing but I'll describe the results.
The generated IL code does the following:
If the first condition is false, jumps to the code where the second is.
If it's true jumps to the last instruction. (Note: the last instruction is a return).
In the second condition the same happens after the result is calculated. Compare and: got to the Console.WriteLine if false or to the end if this is true.
Print the message and return.
So it seems that the code will jump to the end. What if we do a normal if with nested code?
using System;
public class Test {
public static void Main(string[] args) {
if (args.Length != 0 && (args.Length+2)/3 != 5)
{
Console.WriteLine("hey!!!");
}
}
}
The results are quite similar in IL instructions. The difference is that before there were two jumps per condition: if false go to next piece of code, if true go to the end. And now the IL code flows better and has 3 jumps (the compiler optimized this a bit):
First jump: when Length is 0 to a part where the code jumps again (Third jump) to the end.
Second: in the middle of the second condition to avoid one instruction.
Third: if the second condition is false, jump to the end.
Anyway, the program counter will always jump.
In theory, inverting if could lead to better performance if it increases branch prediction hit rate. In practice, I think it is very hard to know exactly how branch prediction will behave, especially after compiling, so I would not do it in my day-to-day development, except if I am writing assembly code.
More on branch prediction here.
That is simply controversial. There is no "agreement among programmers" on the question of early return. It's always subjective, as far as I know.
It's possible to make a performance argument, since it's better to have conditions that are written so they are most often true; it can also be argued that it is clearer. It does, on the other hand, create nested tests.
I don't think you will get a conclusive answer to this question.
There are a lot of insightful answers there already, but still, I would to direct to a slightly different situation: Instead of precondition, that should be put on top of a function indeed, think of a step-by-step initialization, where you have to check for each step to succeed and then continue with the next. In this case, you cannot check everything at the top.
I found my code really unreadable when writing an ASIO host application with Steinberg's ASIOSDK, as I followed the nesting paradigm. It went like eight levels deep, and I cannot see a design flaw there, as mentioned by Andrew Bullock above. Of course, I could have packed some inner code to another function, and then nested the remaining levels there to make it more readable, but this seems rather random to me.
By replacing nesting with guard clauses, I even discovered a misconception of mine regarding a portion of cleanup-code that should have occurred much earlier within the function instead of at the end. With nested branches, I would never have seen that, you could even say they led to my misconception.
So this might be another situation where inverted ifs can contribute to a clearer code.
It's a matter of opinion.
My normal approach would be to avoid single line ifs, and returns in the middle of a method.
You wouldn't want lines like it suggests everywhere in your method but there is something to be said for checking a bunch of assumptions at the top of your method, and only doing your actual work if they all pass.
In my opinion early return is fine if you are just returning void (or some useless return code you're never gonna check) and it might improve readability because you avoid nesting and at the same time you make explicit that your function is done.
If you are actually returning a returnValue - nesting is usually a better way to go cause you return your returnValue just in one place (at the end - duh), and it might make your code more maintainable in a whole lot of cases.
I'm not sure, but I think, that R# tries to avoid far jumps. When You have IF-ELSE, compiler does something like this:
Condition false -> far jump to false_condition_label
true_condition_label:
instruction1
...
instruction_n
false_condition_label:
instruction1
...
instruction_n
end block
If condition is true there is no jump and no rollout L1 cache, but jump to false_condition_label can be very far and processor must rollout his own cache. Synchronising cache is expensive. R# tries replace far jumps into short jumps and in this case there is bigger probability, that all instructions are already in cache.
I think it depends on what you prefer, as mentioned, theres no general agreement afaik.
To reduce annoyment, you may reduce this kind of warning to "Hint"
My idea is that the return "in the middle of a function" shouldn't be so "subjective".
The reason is quite simple, take this code:
function do_something( data ){
if (!is_valid_data( data ))
return false;
do_something_that_take_an_hour( data );
istance = new object_with_very_painful_constructor( data );
if ( istance is not valid ) {
error_message( );
return ;
}
connect_to_database ( );
get_some_other_data( );
return;
}
Maybe the first "return" it's not SO intuitive, but that's really saving.
There are too many "ideas" about clean codes, that simply need more practise to lose their "subjective" bad ideas.
There are several advantages to this sort of coding but for me the big win is, if you can return quick you can improve the speed of your application. IE I know that because of Precondition X that I can return quickly with an error. This gets rid of the error cases first and reduces the complexity of your code. In a lot of cases because the cpu pipeline can be now be cleaner it can stop pipeline crashes or switches. Secondly if you are in a loop, breaking or returning out quickly can save you a lots of cpu. Some programmers use loop invariants to do this sort of quick exit but in this you can broke your cpu pipeline and even create memory seek problem and mean the the cpu needs to load from outside cache. But basically I think you should do what you intended, that is end the loop or function not create a complex code path just to implement some abstract notion of correct code. If the only tool you have is a hammer then everything looks like a nail.