How can I return NULL from a generic method in C

Question

I have a generic method with this  dummy  code  yes I m aware IList has predicates  but my code is not using IList but some other collection  anyway this is irrelevant for the question      static T FindThing lt T gt  IList collection  int id  where T   IThing  new         foreach T thing in collecion               if  thing Id    id              return thing            return null      ERROR  Cannot convert null to type parameter  T  because it could be a value type  Consider using  default T   instead      This gives me a build error       Cannot convert null to type parameter    T  because it could be a value type    Consider using  default T   instead     Can I avoid this error

User · Answer

For me it is works as it is  Where exactly is problem   public static T FindThing lt T gt  this IList collection  int id  where T   IThing  new         foreach  T thing in collection                if  thing Id    id              return thing                       return null    work     return  T null    work     return null as T    work     return default T     work

User · Answer

Your other option would be to to add this to the end of your declaration       where T   class     where T  IList   That way it will allow you to return null

User · Answer

Take the recommendation of the error    and either user default T  or new T   You will have to add in a comparison in your code to ensure that it was a valid match if you go that route   Otherwise  potentially consider an output parameter for  match found

User · Answer

Here s a working example for Nullable Enum return values   public static TEnum  ParseOptional lt TEnum gt  this string value  where TEnum   struct       return value    null    TEnum  null    TEnum  Enum Parse typeof TEnum   value

User · Answer

Below are the two option you can use  return default T     or  where T   class  IThing  return null

User · Answer

You can just adjust your constraints   where T   class   Then returning null is allowed

User · Answer

Add the class constraint as the first constraint to your generic type   static T FindThing lt T gt  IList collection  int id  where T   class  IThing  new

User · Answer

solution of TheSoftwareJedi works   also you can archive it with using couple of value and nullable types   static T  FindThing lt T gt  IList collection  int id  where T   struct  IThing       foreach T thing in collecion               if  thing Id    id              return thing            return null

User · Answer

Two options    Return default T  which means you ll return null if T is a reference type  or a nullable value type   0 for int    0  for char  etc   Default values table  C  Reference   Restrict T to be a reference type with the where T   class constraint and then return null as normal

User · Answer

For completeness sake  it s good to know you could also do this   return default    It returns the same as return default T

User · Answer

For completeness sake  it s good to know you could also do this   return default    It returns the same as return default T

User · Answer

solution of TheSoftwareJedi works   also you can archive it with using couple of value and nullable types   static T  FindThing lt T gt  IList collection  int id  where T   struct  IThing       foreach T thing in collecion               if  thing Id    id              return thing            return null

User · Answer

For me it is works as it is  Where exactly is problem   public static T FindThing lt T gt  this IList collection  int id  where T   IThing  new         foreach  T thing in collection                if  thing Id    id              return thing                       return null    work     return  T null    work     return null as T    work     return default T     work

User · Answer

Two options    Return default T  which means you ll return null if T is a reference type  or a nullable value type   0 for int    0  for char  etc   Default values table  C  Reference   Restrict T to be a reference type with the where T   class constraint and then return null as normal

User · Answer

Another alternative to 2 answers presented above  If you change your return type to object  you can return null  while at the same time cast the non-null return   static object FindThing lt T gt  IList collection  int id        foreach T thing in collecion               if  thing Id    id              return  T  thing            return null      allowed now

User · Answer

Add the class constraint as the first constraint to your generic type   static T FindThing lt T gt  IList collection  int id  where T   class  IThing  new

User · Answer

return default T

User · Answer

Another alternative to 2 answers presented above  If you change your return type to object  you can return null  while at the same time cast the non-null return   static object FindThing lt T gt  IList collection  int id        foreach T thing in collecion               if  thing Id    id              return  T  thing            return null      allowed now

User · Answer

You can just adjust your constraints   where T   class   Then returning null is allowed

User · Answer

Your other option would be to to add this to the end of your declaration       where T   class     where T  IList   That way it will allow you to return null

User · Answer

return default T

User · Answer

Your other option would be to to add this to the end of your declaration       where T   class     where T  IList   That way it will allow you to return null

User · Answer

You can just adjust your constraints   where T   class   Then returning null is allowed

User · Answer

Add the class constraint as the first constraint to your generic type   static T FindThing lt T gt  IList collection  int id  where T   class  IThing  new

User · Answer

Take the recommendation of the error    and either user default T  or new T   You will have to add in a comparison in your code to ensure that it was a valid match if you go that route   Otherwise  potentially consider an output parameter for  match found

User · Answer

If you have object then need to typecast      return  T  object  employee    if you need to return null    return default T

User · Answer

Take the recommendation of the error    and either user default T  or new T   You will have to add in a comparison in your code to ensure that it was a valid match if you go that route   Otherwise  potentially consider an output parameter for  match found

User · Answer

Your other option would be to to add this to the end of your declaration       where T   class     where T  IList   That way it will allow you to return null

User · Answer

Take the recommendation of the error    and either user default T  or new T   You will have to add in a comparison in your code to ensure that it was a valid match if you go that route   Otherwise  potentially consider an output parameter for  match found

User · Answer

Here s a working example for Nullable Enum return values   public static TEnum  ParseOptional lt TEnum gt  this string value  where TEnum   struct       return value    null    TEnum  null    TEnum  Enum Parse typeof TEnum   value

User · Answer

return default T

User · Answer

Two options    Return default T  which means you ll return null if T is a reference type  or a nullable value type   0 for int    0  for char  etc   Default values table  C  Reference   Restrict T to be a reference type with the where T   class constraint and then return null as normal

User · Answer

If you have object then need to typecast      return  T  object  employee    if you need to return null    return default T

User · Answer

You can just adjust your constraints   where T   class   Then returning null is allowed

User · Answer

Add the class constraint as the first constraint to your generic type   static T FindThing lt T gt  IList collection  int id  where T   class  IThing  new

User · Answer

Below are the two option you can use  return default T     or  where T   class  IThing  return null

User · Answer

Two options    Return default T  which means you ll return null if T is a reference type  or a nullable value type   0 for int    0  for char  etc   Default values table  C  Reference   Restrict T to be a reference type with the where T   class constraint and then return null as normal

User · Answer

return default T

[c#] How can I return NULL from a generic method in C#?

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