Filter method without filter parameters doesn't make sense (clarification)

[JakenVeina]

Can I ask for some clarification on what you said in #219? I had the same question and found the issue, but I don't see how the answer explains anything about the question.

Reapply filter is an option which can be used when filtering on mutable values.

But WHAT is the filtering when using this overload, that doesn't specify a filter?

I recommend you down load this DynamicData Snippets where there are some examples of dd filtering + unit tests to illustrate expectations

There's no examples in that project that demonstrate using this overload of .Filter(), with only a reapplyFilter parameter. Not that I could find.

I thought maybe this might be referring to filtering applied when you use .Connect() with the overload that takes a filter parameter, so I tried it out, and reapplyFilter doesn't cause the filtering to reapply. Same thing if I just use an adjacent call to .Filter() either before or after the one with reapplyFilter.

public record ResourceVersionEntity
{
    public required ulong Id { get; init; }

    public required ulong ResourceId { get; init; }

    public ulong? PreviousId { get; init; }

    public required string Name { get; init; }
}

var resourceVersions = new SourceCache<ResourceVersionEntity, ulong>(resourceVersion => resourceVersion.Id);

var previousIdIndex = resourceVersions
    .Connect(resourceVersion => resourceVersion.PreviousId.HasValue)
    .Group(resourceVersion => resourceVersion.PreviousId!.Value)
    .AsObservableCache();

var currentResourceVersions = resourceVersions
    .Connect(resourceVersion => !previousIdIndex.Lookup(resourceVersion.Id).HasValue)
    .Filter(previousIdIndex.Connect().Select(static _ => Unit.Default))
    .ChangeKey(resourceVersion => resourceVersion.ResourceId)
    .AsObservableCache();

resourceVersions.AddOrUpdate(new ResourceVersionEntity()
{
    Id          = 4,
    ResourceId  = 2,
    PreviousId  = 2,
    Name        = "My Renamed Resource"
});

resourceVersions.AddOrUpdate(new ResourceVersionEntity()
{
    Id          = 1,
    ResourceId  = 1,
    Name        = "My Resource"
});

resourceVersions.AddOrUpdate(new ResourceVersionEntity()
{
    Id          = 2,
    ResourceId  = 2,
    Name        = "My Other Resource"
});

resourceVersions.AddOrUpdate(new ResourceVersionEntity()
{
    Id          = 3,
    ResourceId  = 3,
    Name        = "My Additional Resource"
});

resourceVersions.AddOrUpdate(new ResourceVersionEntity()
{
    Id          = 5,
    ResourceId  = 2,
    PreviousId  = 4,
    Name        = "My Restored Resource"
});

[JakenVeina]

I probably should have just done this in the first place. Looking at the source, this operator can literally never emit any items, no matter what parameters you give it.

This overload was originally added by 3657fee, where @RolandPheasant was doing a large scale re-organization, which included consolidating code for all the different .Filter() overloads into the shared StaticFilter and DynamicFilter internal classes, and it looks like he just took an effort to add overloads for all different combinations of optional parameters, without considering that predicateChanged isn't actually an optional parameter.

Seems like this overload should probably just be removed.

[RolandPheasant]

I have to be honest, I really cannot remember the details or the thought process! However having an overload without params is almost certainly a mistake / oversight.

[dwcullop]

Yeah, I can't imagine what that would mean either.