Which is better return value or out parameter

Question

If we want to get a value from a method  we can use either return value  like this   public int GetValue       or   public void GetValue out int x     I don t really understand the differences between them  and so  don t know which is better  Can you explain me this   Thank you

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What s better  depends on your particular situation  One of the reasons out exists is to facilitate returning multiple values from one method call   public int ReturnMultiple int input  out int output1  out int output2        output1   input   1      output2   input   2       return input      So one is not by definition better than the other  But usually you d want to use a simple return  unless you have the above situation for example   EDIT  This is a sample demonstrating one of the reasons that the keyword exists  The above is in no way to be considered a best practise

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I suspect I m not going to get a look-in on this question  but I am a very experienced programmer  and I hope some of the more open-minded readers will pay attention   I believe that it suits object-oriented programming languages better for their value-returning procedures  VRPs  to be deterministic and pure    VRP  is the modern academic name for a function that is called as part of an expression  and has a return value that notionally replaces the call during evaluation of the expression  E g  in a statement such as x   1   f y  the function f is serving as a VRP    Deterministic  means that the result of the function depends only on the values of its parameters  If you call it again with the same parameter values  you are certain to get the same result    Pure  means no side-effects  calling the function does nothing except computing the result  This can be interpreted to mean no important side-effects  in practice  so if the VRP outputs a debugging message every time it is called  for example  that can probably be ignored   Thus  if  in C   your function is not deterministic and pure  I say you should make it a void function  in other words  not a VRP   and any value it needs to return should be returned in either an out or a ref parameter   For example  if you have a function to delete some rows from a database table  and you want it to return the number of rows it deleted  you should declare it something like this   public void DeleteBasketItems BasketItemCategory category  out int count     If you sometimes want to call this function but not get the count  you could always declare an overloading   You might want to know why this style suits object-oriented programming better  Broadly  it fits into a style of programming that could be  a little imprecisely  termed  procedural programming   and it is a procedural programming style that fits object-oriented programming better   Why  The classical model of objects is that they have properties  aka attributes   and you interrogate and manipulate the object  mainly  through reading and updating those properties  A procedural programming style tends to make it easier to do this  because you can execute arbitrary code in between operations that get and set properties   The downside of procedural programming is that  because you can execute arbitrary code all over the place  you can get some very obtuse and bug-vulnerable interactions via global variables and side-effects   So  quite simply  it is good practice to signal to someone reading your code that a function could have side-effects by making it non-value returning

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Both of them have a different purpose and are not treated the same by the compiler  If your method needs to return a value  then you must use return  Out is used where your method needs to return multiple values   If you use return  then the data is first written to the methods stack and then in the calling method s  While in case of out  it is directly written to the calling methods stack  Not sure if there are any more differences

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There s one reason to use an out param which has not already been mentioned  the calling method is obliged to receive it   If your method produces a value which the caller should not discard  making it an out forces the caller to specifically accept it    Method1        Return values can be discard quite easily  even accidentally   int  resultCode   Method2 out resultCode       Out params are a little harder to ignore   Of course the caller can still ignore the value in an out param  but you ve called their attention to it   This is a rare need  more often  you should use an exception for a genuine problem or return an object with state information for an  FYI   but there could be circumstances where this is important

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There is no real difference  Out parameters are in C  to allow method return more then one value  that s all   However There are some slight differences   but non of them are really important   Using out parameter will enforce you to use two lines like   int n  GetValue n     while using return value will let you do it in one line   int n   GetValue      Another difference  correct only for value types and only if C  doesn t inline the function  is that using return value will necessarily make a copy of the value when the function return  while using OUT parameter will not necessarily do so

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You can only have one return value whereas you can have multiple out parameters   You only need to consider out parameters in those cases   However  if you need to return more than one parameter from your method  you probably want to look at what you re returning from an OO approach and consider if you re better off return an object or a struct with these parameters  Therefore you re back to a return value again

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out is more useful when you are trying to return an object that you declare in the method   Example  public BookList Find string key       BookList book    BookList is a model class     books TryGetValue key  out book     books is a concurrent dictionary                                        TryGetValue gets an item with matching key and returns it into book     return book

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I would prefer the following instead of either of those in this simple example   public int Value       get      private set      But  they are all very much the same  Usually  one would only use  out  if they need to pass multiple values back from the method  If you want to send a value in and out of the method  one would choose  ref   My method is best  if you are only returning a value  but if you want to pass a parameter and get a value back one would likely choose your first choice

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Using the out keyword with a return type of bool  can sometimes reduce code bloat and increase readability   Primarily when the extra info in the out param is often ignored   For instance   var result   DoThing    if  result Success        result   DoOtherThing       if  result Success                result   DoFinalThing           if  result Success                        success   true                      vs   var result  if  DoThing out result         if  DoOtherThing out result                 if  DoFinalThing out result                         success   true

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return value is the normal value which is returned by your method   Where as out parameter  well out and ref are 2 key words of C  they allow to pass variables as reference    The big difference between ref and out is  ref should be initialised before and out don t

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I think one of the few scenarios where it would be useful would be when working with unmanaged memory  and you want to make it obvious that the  returned  value should be disposed of manually  rather than expecting it to be disposed of on its own

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It s preference mainly  I prefer returns and if you have multiple returns you can wrap them in a Result DTO  public class Result    public Person Person  get set     public int Sum  get set

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Return values are almost always the right choice when the method doesn t have anything else to return   In fact  I can t think of any cases where I d ever want a void method with an out parameter  if I had the choice  C  7 s Deconstruct methods for language-supported deconstruction acts as a very  very rare exception to this rule    Aside from anything else  it stops the caller from having to declare the variable separately   int foo  GetValue out foo     vs  int foo   GetValue      Out values also prevent method chaining like this   Console WriteLine GetValue   ToString  g        Indeed  that s one of the problems with property setters as well  and it s why the builder pattern uses methods which return the builder  e g  myStringBuilder Append xxx  Append yyy     Additionally  out parameters are slightly harder to use with reflection and usually make testing harder too   More effort is usually put into making it easy to mock return values than out parameters   Basically there s nothing I can think of that they make easier     Return values FTW   EDIT  In terms of what s going on     Basically when you pass in an argument for an  out  parameter  you have to pass in a variable   Array elements are classified as variables too   The method you call doesn t have a  new  variable on its stack for the parameter - it uses your variable for storage  Any changes in the variable are immediately visible  Here s an example showing the difference   using System   class Test       static int value       static void ShowValue string description                Console WriteLine description   value              static void Main                 Console WriteLine  Return value test               value   5          value   ReturnValue            ShowValue  Value after ReturnValue                 value   5          Console WriteLine  Out parameter test               OutParameter out value           ShowValue  Value after OutParameter                   static int ReturnValue                 ShowValue  ReturnValue  pre               int tmp   10          ShowValue  ReturnValue  post               return tmp             static void OutParameter out int tmp                ShowValue  OutParameter  pre               tmp   10          ShowValue  OutParameter  post                 Results   Return value test    ReturnValue  pre   5 ReturnValue  post   5 Value after ReturnValue    10 Out parameter test    OutParameter  pre   5 OutParameter  post   10 Value after OutParameter    10   The difference is at the  post  step - i e  after the local variable or parameter has been changed  In the ReturnValue test  this makes no difference to the static value variable  In the OutParameter test  the value variable is changed by the line tmp   10

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As others have said  return value  not out param   May I recommend to you the book  Framework Design Guidelines   2nd ed    Pages 184-185 cover the reasons for avoiding out params   The whole book will steer you in the right direction on all sorts of  NET coding issues   Allied with Framework Design Guidelines is the use of the static analysis tool  FxCop   You ll find this on Microsoft s sites as a free download   Run this on your compiled code and see what it says   If it complains about hundreds and hundreds of things    don t panic   Look calmly and carefully at what it says about each and every case   Don t rush to fix things ASAP   Learn from what it is telling you   You will be put on the road to mastery

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Additionally  return values are compatible with asynchronous design paradigms    You cannot designate a function  async  if it uses ref or out parameters   In summary  Return Values allow method chaining  cleaner syntax  by eliminating the necessity for the caller to declare additional variables   and allow for asynchronous designs without the need for substantial modification in the future

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You should generally prefer a return value over an out param  Out params are a necessary evil if you find yourself writing code that needs to do 2 things  A good example of this is the Try pattern  such as Int32 TryParse    Let s consider what the caller of your two methods would have to do  For the first example I can write this     int foo   GetValue      Notice that I can declare a variable and assign it via your method in one line  FOr the 2nd example it looks like this     int foo  GetValue out foo     I m now forced to declare my variable up front and write my code over two lines   update  A good place to look when asking these types of question is the  NET  Framework Design Guidelines  If you have the book version then you can see the annotations by Anders Hejlsberg and others on this subject  page 184-185  but the online version is here     http   msdn microsoft com en-us library ms182131 VS 80  aspx  If you find yourself needing to return two things from an API then wrapping them up in a struct class would be better than an out param

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You should almost always use a return value   out  parameters create a bit of friction to a lot of APIs  compositionality  etc   The most noteworthy exception that springs to mind is when you want to return multiple values   Net Framework doesn t have tuples until 4 0   such as with the TryParse pattern

[c#] Which is better, return value or out parameter?

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