C Return Different Types

Question

I got something like this   public  What Here   GetAnything          Hello hello   new Hello         Computer computer   new Computer         Radio radio   new Radio          return radio  or return computer  or return hello   should be possible             I have a Method and this method returns me sometimes different Types of Values  classes     How can I do this anyway and ofcourse later to work with the variables  b e radio Play    and so far    Do I need to use generics  How

User · Answer

You have a few options depending on why you want to return different types.

a) You can just return an object, and the caller can cast it (possibly after type checks) to what they want. This means of course, that you lose a lot of the advantages of static typing.

b) If the types returned all have a 'requirement' in common, you might be able to use generics with constriants.

c) Create a common interface between all of the possible return types and then return the interface.

d) Switch to F# and use pattern matching and discriminated unions. (Sorry, slightly tongue in check there!)

User · Answer

It s a sample using Generic Types   public T GetAnything lt T gt    where T   class  new         gt  new T      And you ll use this method calling this way   var hello   GetAnything lt Hello gt       In this case  you can use an interface to specify a type to pass as parameter   public T GetAnything lt T gt    where T   ISomeInterface  new         gt  new T      You must have a parameterless construtor in each class to use new   constraint   Follow the full sample   internal sealed class Program       private static void Main string   args                GetAnything lt Hello gt    Play            GetAnything lt Radio gt    Play            GetAnything lt Computer gt    Play               private static T GetAnything lt T gt    where T   ISomeInterface  new             gt  new T       internal interface ISomeInterface       void Play       internal sealed class Hello   ISomeInterface          parameterless constructor      public Hello           public void Play     gt  Console WriteLine  Saying hello        internal sealed class Radio   ISomeInterface          parameterless constructor      public Radio           public void Play     gt  Console WriteLine  Playing radio        internal sealed class Computer   ISomeInterface          parameterless constructor      public Computer           public void Play     gt  Console WriteLine  Playing from computer

User · Answer

Here is how you might do it with generics   public T GetAnything lt T gt         T t     Code to create instance     return t      But you would have to know what type you wanted returned at design time   And that would mean that you could just call a different method for each creation

User · Answer

Rick s solution is the  best  way to go in most cases  Sometimes when that s not available you want to use object as base type  And you could use the method like this   public object GetAnything          Hello hello   new Hello         Computer computer   new Computer         Radio radio   new Radio          return hello     or computer or radio        To use it  you will want to use the as operator  like this   public void TestMethod         object anything   GetAnything        var hello   anything as Hello      var computer   anything as Computer      var radio   anything as Radio       if  hello    null                   GetAnything   returned a hello           else if  computer    null                   GetAnything   returned a computer           else if  radio    null                   GetAnything   returned a radio           else                  GetAnything   returned    well anything  D           In your case you want to call a method play  So this d seem more appropriate   interface IPlayable       void Play       class Radio   IPlayable       public void Play        Play radio         class Hello   IPlayable       public void Play        Say hello         class Computer   IPlayable       public void Play        beep beep         public IPlayable GetAnything          Hello hello   new Hello         Computer computer   new Computer         Radio radio   new Radio          return hello     or computer or radio

User · Answer

use the dynamic keyword as return type    private dynamic getValuesD lt T gt                  if  typeof T     typeof int                         return 0                    else if  typeof T     typeof string                         return                       else if  typeof T     typeof double                         return 0                    else                       return false                           int res   getValuesD lt int gt             string res1   getValuesD lt string gt             double res2   getValuesD lt double gt             bool res3   getValuesD lt bool gt          dynamic keyword is preferable to use in this case instead of an object type     because dynamic keyword keeps the underlying structure and data type so that    you can directly inspect and view the value      in object type  you have to cast the object to a specific data type to view    the underlying value    regards   Abhijit

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You can have the return type to be a superclass of the three classes  either defined by you or just use object   Then you can return any one of those objects  but you will need to cast it back to the correct type when getting the result  Like   public object GetAnything          Hello hello   new Hello         Computer computer   new Computer         Radio radio   new Radio          return radio  or return computer  or return hello   should be possible             Then   Hello hello    Hello getAnything

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Defining a single type for all is not always possible  Even if when you can  the implementation is rarely easy  I prefer to use out parameters  The only caveat is that you need to know all the return types in advanced   public void GetAnything out Hello h  out Computer c  out Radio r             I suggest to       h   null       c   null       r   null           first            Then do whatever you have to do       Hello hello   new Hello         Computer computer   new Computer         Radio radio   new Radio        The return type can be a void  or something else  like bool an int or a predefined enum which can help you check for exceptions or different cases wherever the method is used

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My post here is strictly related to Blazor v5 but should work in 3 x as well  Additionally  I m using these methods with bootstrap 4 5 and 5 0 beta 1 but you could easily adapt it to use style s instead of classes or use your own classes  To those recommending dynamic  I thank you  The dynamic type seems like it can be very valuable when used correctly  Most of the time you ll probably use an interface but this wasn t plausible for me  I went ahead and updated my project with a dynamic return type and it s working great while being the quickest  cleanest solution  I previously added the following extension methods to boolean types to help me avoid long ternary operators in razor page code  Here are the 3 main extension methods I use to accomplish it  public static T Then lt T gt  this bool value  T result    gt  value   result   default      public static T Then lt T gt  this bool value  T thenResult  T elseResult    gt  value   thenResult   elseResult  public static T Else lt T gt  this bool value  T result    gt   value   result   default   The following are examples of that implementation   lt div class  quot  Hidden Then  quot d-none quot   quot  gt      Hidden content     lt  div gt   Note  ErrorOrWarning would hide the content if there was no error warning so I could default it to yellow italic but this is an example so please use your imagination   lt div class  quot  ErrorOrWarning Else  quot d-none quot   quot  style  quot  Error Then  quot color red font-weight bold  quot   quot color yellow font-style italic  quot   quot  gt      Error Warning content     lt  div gt   This is the typical implementation without the extension methods  It s common to see this technique in Blazor guides tutorials videos online  There are cleaner ways to handle it but this is the basic idea   lt div class  quot   ErrorOrWarning    quot  quot     quot d-none quot   quot  style  quot   Error    quot color red font-weight bold  quot     quot color yellow font-style italic  quot   quot  gt      Error Warning content     lt  div gt   While this might not seem like too big a difference  if you have a lot of dynamic content styles driving your page  it can get really messy  With those 3 lines of code you can enhance the readability and cleanliness and it really does reduce risk of typos  Adding two more extension methods  you can reduce the risk even further Note  Again  this is using bootstrap class  quot d-none quot  for the style  quot display none important quot  but you could just as easily replace with your own usage  public static string ThenShow this bool value    gt  value    quot  quot     quot d-none quot   public static string ThenHide this bool value    gt  value    quot d-none quot     quot  quot    The limitation I previously faced was when using the overloaded Then thenResult  elseResult   each of the parameters must be of the same type  99  of the time this is fine  Actually  another 0 5  of the time it s still okay because you can probably solve it quickly with a  ToString   or an explicit cast  What I ran into  and what took me to this post was  I have a control you can imagine as a button  There is an Enum property allowing the user to select an icon to display  The selected Enum dynamically populates a readonly MarkupString property  As an alternative option  they can use the ChildContent  or IconContent in my example  of type RenderFragment  This will let them manually add anything they want  maybe an iFrame to stackoverflow haha  but my intention is for them to add style  most likely in the form of an icon  I know I can cast convert one to the other however my existing extension method is so clean and simple  it would be great to be able to use pass the MarkupString and RenderFragment together as parameters  conditionally output to the razor page  So  thanks to this post  I changed my Then thenResult  elseResult  extension methods to use unique generic parameter types and return a dynamic type like so  public static dynamic Then lt T E gt  this bool value  T thenResult  E elseResult    gt  value   thenResult   elseResult   Now in my razor page I have a very simple line for the icon output  Note  IconContent is a RenderFragment and IconMarkup is a MarkupString      IconContent    null  Then IconMarkup  IconContent    And because I love extension methods and I m typing this up  I took it a step further with another extension method  public static bool IsNull this RenderFragment value    gt  value    null   Which enables the extremely clean and simple   IconContent IsNull   Then IconMarkup  IconContent   Here s the extra extension method I mentioned above which converts a string to a MarkupString  It might be overkill but I like it  public static MarkupString ToMarkup this string value    gt   MarkupString value   Let me know if you have a better recommendation or if you think I m doing something wrong  I m sure this post makes it seem like I overuse extension methods but I really don t  I keep their use limited to outcomes such as I ve outlined in this post

User · Answer

To build on the answer by  RQDQ using generics  you can combine this with Func lt TResult gt   or some variation  and delegate responsibility to the caller   public T GetAnything lt T gt  Func lt T gt  createInstanceOfT          do whatever      return createInstanceOfT        Then you can do something like   Computer comp   GetAnything      gt  new Computer     Radio rad   GetAnything      gt  new Radio

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Let the method return a object from a common baseclass or interface   public class TV IMediaPlayer      void Play         public class Radio IMediaPlayer      void Play         public interface IMediaPlayer      void Play       public class Test     public void Main            IMediaPlayer player   GetMediaPlayer         player Play            private IMediaPlayer GetMediaPlayer            if              return new TV         else         return new Radio

User · Answer

If there is no common base-type or interface  then public object GetAnything         - but it would usually be preferable to have some kind of abstraction such as a common interface  For example if Hello  Computer and Radio all implemented IFoo  then it could return an IFoo

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May be you need  dynamic  type   public dynamic GetAnything          Hello hello   new Hello         Computer computer   new Computer         Radio radio   new Radio          return   what boject you needed     enter code here

User · Answer

You could use external class  set the properties types as you wish  then use it in your function   public class MultipleOpjects       private List lt string gt   ObjectOne      public List lt string gt  ObjectOne           get   return  ObjectOne            set    ObjectOne   value              private List lt object gt   ObjectTwo      public List lt object gt  ObjectTwo           get   return  ObjectTwo            set    ObjectTwo   value              private object  ObjectThree      public object ObjectThree           get   return  ObjectThree            set    ObjectThree   value            public MultipleOpjects GetAnything         MultipleOpjects Vrble   new MultipleOpjects        Vrble ObjectOne    SomeThing1      Vrble ObjectTwo   SomeThing2      Vrble ObjectThree   SomeThing3       return Vrble

User · Answer

You could just return an Object as all types are descended from Object   public Object GetAnything          Hello hello   new Hello         Computer computer   new Computer         Radio radio   new Radio          return radio  or return computer  or return hello   should be possible             You could then cast to its relevant type   Hello hello    Hello GetAnything      If you didn t know what the type was going to be then you could use the is keyword   Object obj   GetAnything    if  obj is Hello           Do something     This being said I would be reluctant to write code like that  It would be much better to have an interface which is implemented by each of your classes   public ISpeak GetAnything          Hello hello   new Hello         Computer computer   new Computer         Radio radio   new Radio          return radio  or return computer  or return hello   should be possible            interface ISpeak       void Speak        and have each of your classes implement the interface   public class Hello   ISpeak       void Speak             Console WriteLine  Hello              You could then do something like   GetAnything   Speak

User · Answer

Marc s answer should be the correct one  but in  NET 4 you couldn t also go with dynamic type   This should be used only if you have no control over the classes you return and there are no common ancestors   usually with interop   and only if not using dynamic is a lot more painful then using casting every object in every step        Few blog post trying to explain when to use dynamic  http   blogs msdn com b csharpfaq archive tags dynamic   public dynamic GetSomething          Hello hello   new Hello         Computer computer   new Computer         Radio radio   new Radio          return    anyobject

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If you can make a abstract class for all the possibilities then that is highly recommended   public Hardware GetAnything          Computer computer   new Computer          return computer         abstract Hardware       class Computer   Hardware        Or an interface   interface IHardware       class Computer   IHardware        If it can be anything then you could consider using  object  as your return type  because every class derives from object   public object GetAnything          Hello hello   new Hello          return hello

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