Collection that allows only unique items in NET

Question

Is there a collection in C  that will not let you add duplicate items to it  For example  with the silly class of  public class Customer       public string FirstName   get  set        public string LastName   get  set        public string Address   get  set         public override int GetHashCode             return  FirstName   LastName   Address  GetHashCode               public override bool Equals object obj            Customer C   obj as Customer          return C    null  amp  amp  String Equals this FirstName  C FirstName   amp  amp  String Equals this LastName  C LastName   amp  amp  String Equals this Address  C Address             The following code will  obviously  throw an exception   Customer Adam   new Customer   Address    A   FirstName    Adam   LastName         Customer AdamDup   new Customer   Address    A   FirstName    Adam   LastName          Dictionary lt Customer  bool gt  CustomerHash   new Dictionary lt Customer  bool gt     CustomerHash Add Adam  true   CustomerHash Add AdamDup  true     But is there a class that will similarly guarantee uniqueness  but without KeyValuePairs  I thought HashSet lt T gt  would do that  but having read the docs it seems that class is just a set implementation  go figure

User · Accepted Answer

HashSet lt T gt  is what you re looking for  From MSDN  emphasis added       The HashSet lt T gt  class provides high-performance set operations  A set is a collection that contains no duplicate elements  and whose elements are in no particular order    Note that the HashSet lt T gt  Add T item  method returns a bool -- true if the item was added to the collection  false if the item was already present

User · Answer

Just to add my 2 cents     if you need a ValueExistingException-throwing HashSet lt T gt  you can also create your collection easily   public class ThrowingHashSet lt T gt    ICollection lt T gt        private HashSet lt T gt  innerHash   new HashSet lt T gt          public void Add T item                if   innerHash Add item               throw new ValueExistingException               public void Clear                 innerHash Clear               public bool Contains T item                return innerHash Contains item              public void CopyTo T   array  int arrayIndex                innerHash CopyTo array  arrayIndex              public int Count               get   return innerHash Count               public bool IsReadOnly               get   return false               public bool Remove T item                return innerHash Remove item              public IEnumerator lt T gt  GetEnumerator                 return innerHash GetEnumerator               System Collections IEnumerator System Collections IEnumerable GetEnumerator                 return this GetEnumerator              this can be useful for example if you need it in many places

User · Answer

From the HashSet lt T gt  page on MSDN      The HashSet Of T  class provides high-performance set operations  A set is a collection that contains no duplicate elements  and whose elements are in no particular order     emphasis mine

User · Answer

You can try HashSet lt T gt

User · Answer

If all you need is to ensure uniqueness of elements  then HashSet is what you need    What do you mean when you say  just a set implementation   A set is  by definition  a collection of unique elements that doesn t save element order

User · Answer

You may look into something kind of Unique List as follows  public class UniqueList lt T gt        public List lt T gt  List               get          private set            List lt T gt   internalList       public static UniqueList lt T gt  NewList               get                       return new UniqueList lt T gt                          private UniqueList                              internalList   new List lt T gt             List   new List lt T gt                public void Add T value                List Clear             internalList Add value           List AddRange  internalList Distinct               return List             public void Add params T   values                List Clear             internalList AddRange values           List AddRange  internalList Distinct               return List             public bool Has T value                return List Contains value             and you can use it like follows  var uniquelist   UniqueList lt string gt  NewList  uniquelist Add  abc   def   ghi   jkl   mno    uniquelist Add  abc   jkl    var  myList   uniquelist List    will only return  abc   def   ghi   jkl   mno  always even when duplicates are added to it

User · Answer

How about just an extension method on HashSet   public static void AddOrThrow lt T gt  this HashSet lt T gt  hash  T item        if   hash Add item           throw new ValueExistingException

[c#] Collection that allows only unique items in .NET?

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