c# - ImmutableHashSet .Contains returns false -

i have list (to precise immutablehashset<listitem> system.collections.immutable) of base items , try call following code

_baselist.contains(deriveditem) 

but returns false.

even though following code lines return true

object.referenceequals(_baselist.first(), deriveditem) object.equals(_baselist.first(), deriveditem) _baselist.first().gethashcode() == deriveditem.gethashcode() 

i can write following , returns true:

_baselist.oftype<derivedclass>().contains(deriveditem) 

what doing wrong, avoid writing .oftype stuff.

edit:

private immutablehashset<baseclass> _baselist;  public class baseclass {  }  public class derivedclass : baseclass {  }  public void dostuff() {     var items = _baselist.oftype<derivedclass>().tolist();     foreach (var deriveditem in items)     {         removeitem(deriveditem);     } }  public void removeitem(baseclass deriveditem) {     if (_baselist.contains(deriveditem))     {         //doesn't reach place, since _baselist.contains(deriveditem) returns false...         _baselist = _baselist.remove(deriveditem);     }      //object.referenceequals(_baselist.first(), deriveditem) == true     //object.equals(_baselist.first(), deriveditem) == true     //_baselist.first().gethashcode() == deriveditem.gethashcode() == true     //_baselist.oftype<derivedclass>().contains(deriveditem) == true } 

edit2:

here reproducible code of problem, seems immutablehashset<> caches gethashcode , doesn't compare current gethashcode entries inside list, there way tell immutablehashset<> gethashcode of items different, atleast item checking since hey damn same reference...

namespace consoleapplication1 {     class program     {         private static immutablehashset<baseclass> _baselist;          static void main(string[] args)         {             _baselist = immutablehashset.create<baseclass>();             _baselist = _baselist.add(new derivedclass("b1"));             _baselist = _baselist.add(new derivedclass("b2"));             _baselist = _baselist.add(new derivedclass("b3"));             _baselist = _baselist.add(new derivedclass("b4"));             _baselist = _baselist.add(new derivedclass("b5"));              dostuff();             console.writeline(_baselist.count); //output 5 - put should 0...             console.readline();         }          private static void dostuff()         {             var items = _baselist.oftype<derivedclass>().tolist();             foreach (var deriveditem in items)             {                 deriveditem.basestring += "change...";                 removeitem(deriveditem);             }         }          private static void removeitem(baseclass deriveditem)         {             if (_baselist.contains(deriveditem))             {                 _baselist = _baselist.remove(deriveditem);             }         }     }      public abstract class baseclass     {         private string _basestring;         public string basestring         {             { return _basestring; }             set { _basestring = value; }         }          public baseclass(string basestring)         {             _basestring = basestring;         }          public override int gethashcode()         {             unchecked             {                 int hashcode = (_basestring != null ? _basestring.gethashcode() : 0);                 return hashcode;             }         }     }     public class derivedclass : baseclass     {         public derivedclass(string basestring)             : base(basestring)         {          }     } } 

if change immutablehashset<> immutablelist<> code works fine, if guys don't come idea switch list.

objects used in dictionaries , other hashing-related data structures should have immutable identity - hashing-related data structures assume once add object dictionary, hashcode not going change.

this code not going work:

    private static void dostuff()     {         var items = _baselist.oftype<derivedclass>().tolist();         foreach (var deriveditem in items)         {             deriveditem.basestring += "change...";             removeitem(deriveditem);         }     }      private static void removeitem(baseclass deriveditem)     {         if (_baselist.contains(deriveditem))         {             _baselist = _baselist.remove(deriveditem);         }     } 

_baselist.contains() in removeitem(), called dostuff() going return false every single item, because changed identity of stored item - basestring property.