HashSet<T>.Remove doesn't break enumerator

[pkindruk]

Mdsn docs states that enumerator is valid until collection is changed. However it is not true on remove for net5.0, net6.0.

Source code for HashSet<T>.Remove(T item) doesn't increment _version. Is this behavior intended?

Code sample below throws on net472, netcoreapp3.1, but works on net5.0, net6.0.

public class Data
{
    public int Id { get; set; }

    public bool ToRemove { get; set; }
}

static void Main(string[] args)
{
    var set = new HashSet<Data>();

    for (var i = 0; i < 500; i++)
    {
        var removeFlag = i % 2 == 1;
        set.Add(new Data { Id = i, ToRemove = removeFlag });
    }

    var toRemove = set.Where(d => d.ToRemove);
    foreach(var d in toRemove)
    {
        _ = set.Remove(d);
    }

    Console.WriteLine("Success");
    Console.WriteLine(set.Count);
    foreach (var d in set)
        Console.WriteLine(d.Id);
}

Environment:

.NET SDK (reflecting any global.json):
 Version:   6.0.402
 Commit:    6862418796

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19045
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\6.0.402\

global.json file:
  Not found

Host:
  Version:      6.0.11
  Architecture: x64
  Commit:       943474ca16

.NET SDKs installed:
  3.1.425 [C:\Program Files\dotnet\sdk]
  5.0.413 [C:\Program Files\dotnet\sdk]
  6.0.402 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 3.1.31 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 3.1.31 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.31 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 6.0.11 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[stephentoub]

This is by design, for both HashSet and Dictionary. If the docs still say that, they're out of date and should be fixed. We'd welcome a PR to the docs repo. Thanks.

[pkindruk]

Thanks