AddRange to a Collection

Question

A coworker asked me today how to add a range to a collection  He has a class that inherits from Collection lt T gt   There s a get-only property of that type that already contains some items  He wants to add the items in another collection to the property collection  How can he do so in a C 3-friendly fashion   Note the constraint about the get-only property  which prevents solutions like doing Union and reassigning    Sure  a foreach with Property  Add will work  But a List lt T gt -style AddRange would be far more elegant   It s easy enough to write an extension method   public static class CollectionHelpers       public static void AddRange lt T gt  this ICollection lt T gt  destination                                     IEnumerable lt T gt  source                foreach  T item in source                        destination Add item                       But I have the feeling I m reinventing the wheel  I didn t find anything similar in System Linq or morelinq   Bad design  Just Call Add  Missing the obvious

User · Answer

You could add your IEnumerable range to a list then set the ICollection   to the list           IEnumerable lt T gt  source           List lt item gt  list   new List lt item gt             list AddRange source            ICollection lt item gt  destination   list

User · Answer

No  this seems perfectly reasonable   There is a List lt T gt  AddRange   method that basically does just this  but requires your collection to be a concrete List lt T gt

User · Answer

Here is a bit more advanced production-ready version        public static class CollectionExtensions               public static TCol AddRange lt TCol  TItem gt  this TCol destination  IEnumerable lt TItem gt  source              where TCol   ICollection lt TItem gt                        if destination    null  throw new ArgumentNullException nameof destination                if source    null  throw new ArgumentNullException nameof source                    don t cast to IList to prevent recursion             if  destination is List lt TItem gt  list                                list AddRange source                   return destination                             foreach  var item in source                                destination Add item                              return destination

User · Answer

Remember that each Add will check the capacity of the collection and resize it whenever necessary  slower   With AddRange  the collection will be set the capacity and then added the items  faster   This extension method will be extremely slow  but will work

User · Answer

Since  NET4 5 if you want one-liner you can use System Collections Generic ForEach    source ForEach o   gt  destination Add o      or even shorter as  source ForEach destination Add     Performance-wise it s the same as for each loop  syntactic sugar    Also don t try assigning it like  var x   source ForEach destination Add     cause ForEach is void   Edit  Copied from comments  Lipert s opinion on ForEach

User · Answer

The C5 Generic Collections Library classes all support the AddRange method  C5 has a much more robust interface that actually exposes all of the features of its underlying implementations and is interface-compatible with the System Collections Generic ICollection and IList interfaces  meaning that C5 s collections can be easily substituted as the underlying implementation

User · Answer

Or you can just make an ICollection extension like this    public static ICollection lt T gt  AddRange lt T gt  this ICollection lt T gt   this  IEnumerable lt T gt  items                foreach var item in items                         this Add item                      return  this          Using it would be just like using it on a list    collectionA AddRange IEnumerable lt object gt  items

User · Answer

Agree with some guys above and Lipert s opinion  In my case  it s quite often to do like this  ICollection lt int gt  A  var B   new List lt int gt   1 2 3 4 5   B ForEach A Add    To have an extension method for such operation a bit redundant in my view

User · Answer

Try casting to List in the extension method before running the loop  That way you can take advantage of the performance of List AddRange   public static void AddRange lt T gt  this ICollection lt T gt  destination                                 IEnumerable lt T gt  source        List lt T gt  list   destination as List lt T gt        if  list    null                list AddRange source             else               foreach  T item in source                        destination Add item

[c#] AddRange to a Collection

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