C Create New T

Question

You can see what I m trying  but failing  to do with the following code   protected T GetObject         return new T        Any help would be greatly appreciated   EDIT   The context was as follows   I was playing around with a custom controller class for all controllers to derive from  with standardised methods   So in context  I needed to create a new instance of the object of the controller type   So at time of writing  it was something like   public class GenericController lt T gt    Controller                protected T GetObject                 return  T Activator CreateInstance ObjectType                      public ActionResult Create                 var obj   GetObject            return View obj           And so I decided reflection was easiest here   I agree that  certainly given the initial statement of the question  the most appropriate answer to mark as correct was the one using the new   constraint   I have fixed that up

User · Answer

Just for completion  the best solution here is often to require a factory function argument   T GetObject lt T gt  Func lt T gt  factory     return factory        and call it something like this   string s   GetObject      gt   result      You can use that to require or make use of available parameters  if needed

User · Answer

The new constraint is fine  but if you need T being a value type too  use this   protected T GetObject         if  typeof T  IsValueType    typeof T     typeof string             return default T         else          return  T Activator CreateInstance typeof T

User · Answer

Take a look at new Constraint  public class MyClass lt T gt  where T   new         protected T GetObject                 return new T              T could be a class that does not have a default constructor  in this case new T   would be an invalid statement  The new   constraint says that T must have a default constructor  which makes new T   legal   You can apply the same constraint to a generic method   public static T GetObject lt T gt    where T   new         return new T        If you need to pass parameters   protected T GetObject params object   args        return  T Activator CreateInstance typeof T   args

User · Answer

Why hasn t anyone suggested Activator CreateInstance    http   msdn microsoft com en-us library wccyzw83 aspx  T obj    T Activator CreateInstance typeof T

User · Answer

To get this i tried following code      protected T GetObject lt T gt                  T obj   default T           obj  Activator CreateInstance lt T gt             return obj

User · Answer

Another way is to use reflection   protected T GetObject lt T gt  Type   signature  object   args        return  T typeof T  GetConstructor signature  Invoke args

User · Answer

Since this is tagged C  4  With the open sourece framework ImpromptuIntereface it will use the dlr to call the constructor it is significantly faster than Activator when your constructor has arguments  and negligibly slower when it doesn t  However the main advantage is that it will handle constructors with C  4 0 optional parameters correctly  something that Activator won t do   protected T GetObject params object   args        return  T Impromptu InvokeConstructor typeof T   args

[c#] C# Create New T()

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