Bug 5245 - IEquatable<T> , IEqualityComparer<T> are ignored by LinkedList<T>.Find
Summary: IEquatable<T> , IEqualityComparer<T> are ignored by LinkedList<T>.Find
Alias: None
Product: Class Libraries
Classification: Mono
Component: System ()
Version: master
Hardware: PC Windows
: High normal
Target Milestone: Untriaged
Assignee: Marek Safar
Depends on:
Reported: 2012-05-22 14:25 UTC by Ruofeng Lin
Modified: 2014-01-14 08:26 UTC (History)
4 users (show)

Is this bug a regression?: ---
Last known good build:

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Description Ruofeng Lin 2012-05-22 14:25:07 UTC
I recently ported some code from Standard desktop .Net Framework to Mono, and I found some strange behaviour of LinkedList<T>.
It just ignored my custom Equals function, which is the implementation of IEquatable<T> , IEqualityComparer<T> interface.
So I can't find any node by using LinkedList<T>.Find() method.

This worked in standard .net framework.

Then I noticed if I override the non generic Object.Equals(object) function it'll then work.
But I think it is also very important to support IEquatable<T> and IEqualityComparer<T> interface
Comment 1 Jonathan Pryor 2014-01-13 15:10:53 UTC
LinkedList<T>.Find() (and maybe others?) should use EqualityComparer<T>.Default.Equals(T, T), not object.Equals(object):


Sample program:

  using System;
  using System.Collections.Generic;

  class MyValue : IEquatable<MyValue> {
    public readonly string Value;
    public MyValue (string value)
      this.Value = value;
    public bool Equals (MyValue other)
      if (other == null)
        return false;
      if (object.ReferenceEquals (this, other))
        return true;
      return string.Equals (Value, other.Value,

  class TEst {
    public static void Main ()
      var list = new LinkedList<MyValue> ();
      list.AddFirst (new MyValue ("first"));
      var expected = new MyValue ("FIRST");
      var n = list.Find (expected);
      if (n == null)
        throw new InvalidOperationException ("Expected MyValue!");
      Console.WriteLine (n);

Expected behavior: Same as .NET:


Actual behavior:

> Unhandled Exception:
> System.InvalidOperationException: Expected MyValue!
>   at TEst.Main () [0x00000] in <filename unknown>:0
Comment 2 Marek Safar 2014-01-14 08:26:05 UTC
Fixed in master