Collection Expression syntax not compatible with orleans serializer about orleans

[ReubenBond]

Good find, thank you for reporting. It might be time for us to add serializers for unknown collection types. eg, if a type implements IEnumerable<T> but otherwise has no known serializer, enumerate it to a list and serialize it as such. It would solve the issue with returning LINQ queries, too.

[cbgrasshopper]

We encountered a related issue with code like this:

private readonly List<Problem> _problems = [];

public List<Problem> Problems
{
  get
  {
    return _problems;
  }
  set
  {
    _problems.AddRange(value);
  }
}

public Problem Problem
{
  set => _problems.Add(value);
}

When the setter for Problems is called, _problems is null, so AddRange fails. The issue does not occur if we change the private field declaration to this (the remaining code is unchanged):

private readonly List<Problem> _problems = new();

[icanhasjonas]

Adding the expected error here just in case :-)

Orleans.Serialization.CodecNotFoundException: Could not find a codec for type <>z__ReadOnlyArray`1[System.String].

[ReubenBond]

That is surprising behavior, @cbgrasshopper. I don't see any serialization attributes in that code, but I assume this error occurs post-deserialization?

[cbgrasshopper]

@ReubenBond Yes, this is post-deserialization, and yes, this is surprising behavior 🤣 . I didn't include the serialization attributes in my snippet, but they are there as follows:

[GenerateSerializer]
[Alias("CommandOutcome")]
public record CommandOutcome
{
    private readonly List<Problem> _problems = [];

...

    [Id(0)]
    public List<Problem> Problems
    {
        get => _problems;
        set => _problems.AddRange(value);
    }

[cbgrasshopper]

And if we substitute new() for [], everything works as expected.

[cbgrasshopper]

Just discovered that we can also resolve it as follows:

[GenerateSerializer]
[Alias("CommandOutcome")]
public record CommandOutcome
{
    [Id(1)]
    private readonly List<Problem> _problems = [];

...

    [Id(0)]
    public List<Problem> Problems
    {
        get => _problems;
        set => _problems.AddRange(value);
    }

In this case, the collection expression works. Very interesting...

[ReubenBond]

Oh, make sure you only give the field an [Id(...)], and not the property. That is important.
I'm still a little surprised this didn't work, since it looks like your type has a default constructor.

[cbgrasshopper]

It does have a default constructor.

Oh, make sure you only give the field an [Id(...)], and not the property. That is important.

This seems like a worthwhile addition to the Serialization in Orleans documentation.

[icanhasjonas]

This is related - but also pretty much all Frozen collections also are failing on copy/serialization

public Task<IReadOnlySet<string>> ThisWillBreakSerialization() {
  return new HashSet<string> { "Hello World" }.ToFrozenSet();
}