Method call if not null in C

Question

Is it possible to somehow shorten this statement   if  obj    null      obj SomeMethod      because I happen to write this a lot and it gets pretty annoying  The only thing I can think of is to implement Null Object pattern  but that s not what I can do every time and it s certainly not a solution to shorten syntax   And similar problem with events  where   public event Func lt string gt  MyEvent    and then invoke  if  MyEvent    null      MyEvent Invoke

User · Answer

Yes  in C  6 0 -- https   msdn microsoft com en-us magazine dn802602 aspx   object  SomeMethod

User · Answer

Maybe not better but in my opinion more readable is to create an extension method  public static bool IsNull this object obj     return obj    null

User · Answer

A quick extension method       public static void IfNotNull lt T gt  this T obj  Action lt T gt  action  Action actionIfNull   null  where T   class           if obj    null                action obj             else if   actionIfNull    null                 actionIfNull                      example     string str   null    str IfNotNull s   gt  Console Write s Length      str IfNotNull s   gt  Console Write s Length        gt  Console Write  null       or alternatively       public static TR IfNotNull lt T  TR gt  this T obj  Func lt T  TR gt  func  Func lt TR gt  ifNull   null  where T   class           return obj    null   func obj     ifNull    null   ifNull     default TR            example       string str   null      Console Write str IfNotNull s   gt  s Length ToString         Console Write str IfNotNull s   gt  s Length ToString         gt    null

User · Answer

What you re looking for is the Null-Conditional  not  quot coalescing quot   operator      It s available as of C  6  Your example would be obj  SomeMethod     If obj is null  nothing happens  When the method has arguments  e g  obj  SomeMethod new Foo    GetBar     the arguments are not evaluated if obj is null  which matters if evaluating the arguments would have side effects  And chaining is possible  myObject  Items  0   DoSomething

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I have made this generic extension that I use  public static class ObjectExtensions       public static void With lt T gt  this T value  Action lt T gt  todo            if  value    null  todo value            Then I use it like below  string myString   null  myString With  value    gt  Console WriteLine value       writes nothing myString    quot my value quot   myString With  value    gt  Console WriteLine value       Writes  my value

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Cerating extention method like one suggested does not really solve issues with race conditions  but rather hide them   public static void SafeInvoke this EventHandler handler  object sender        if  handler    null  handler sender  EventArgs Empty       As stated this code is the elegant equivalent to solution with temporary variable  but     The problem with both that it s possible that subsciber of the event could be called AFTER it has unsubscribed from the event  This is possible because unsubscription can happen after delegate instance is copied to the temp variable  or passed as parameter in the method above   but before delegate is invoked   In general the behaviour of the client code is unpredictable in such case  component state could not allow to handle event notification already  It s possible to write client code in the way to handle it  but it would put unnecesssary responsibility to the client   The only known way to ensure thread safity is to use lock statement for the sender of the event  This ensures that all subscriptions unsubscriptions invocation are serialized   To be more accurate lock should be applied to the same sync object used in add remove event accessor methods which is be default  this

User · Answer

I agree with the answer by Kenny Eliasson  Go with Extension methods  Here is a brief overview of extension methods and your required IfNotNull method   Extension Methods   IfNotNull method

User · Answer

Events can be initialized with an empty default delegate which is never removed   public event EventHandler MyEvent   delegate        No null-checking necessary    Update  thanks to Bevan for pointing this out   Be aware of the possible performance impact  though  A quick micro benchmark I did indicates that handling an event with no subscribers is 2-3 times slower when using the the  default delegate  pattern   On my dual core 2 5GHz laptop that means 279ms   785ms for raising 50 million not-subscribed events    For application hot spots  that might be an issue to consider

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This article by Ian Griffiths gives two different solutions to the problem that he concludes are neat tricks that you should not use

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From C  6 onwards  you can just use   MyEvent  Invoke      or   obj  SomeMethod      The    is the null-propagating operator  and will cause the  Invoke   to be short-circuited when the operand is null  The operand is only accessed once  so there is no risk of the  value changes between check and invoke  problem        Prior to C  6  no  there is no null-safe magic  with one exception  extension methods - for example   public static void SafeInvoke this Action action        if action    null  action        now this is valid   Action act   null  act SafeInvoke       does nothing act   delegate  Console WriteLine  hi     act SafeInvoke       writes  hi    In the case of events  this has the advantage of also removing the race-condition  i e  you don t need a temporary variable  So normally you d need   var handler   SomeEvent  if handler    null  handler this  EventArgs Empty     but with   public static void SafeInvoke this EventHandler handler  object sender        if handler    null  handler sender  EventArgs Empty       we can use simply   SomeEvent SafeInvoke this      no race condition  no null risk

User · Answer

There is a little-known null operator in C  for this      May be helpful   http   weblogs asp net scottgu archive 2007 09 20 the-new-c-null-coalescing-operator-and-using-it-with-linq aspx

[c#] Method call if not null in C#

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