Feature: Operators for IObservable<Optional<T>>

[dwcullop]

Description

This PR adds some extension methods to IObservable<Optional<T>> to enable the same fluent syntax for IObservable<Optional<T>> that exists for Optional<T>. The operations are the identical to the single Optional versions except they apply to every value that comes through the observable event stream.

Examples Usage

Some basic usage shown below:

// Assume These
IObservable<Optional<string>> GetOptionalStringObservable();
Optional<int> ParseInt(string input) =>
    int.TryParse(input, out var result) ? Optional.Some(result) : Optional.None<int>();
Optional<int> GetFallbackValue();

IObservable<int> intObservable = GetOptionalStringObservable()
                                       .Convert(ParseInt)
                                       .OnHasValue(i => Console.WriteLine("Parsed: " + i.ToString()))
                                       .OrElse(GetFallbackValue);

Combine them with other Observable Optional functionality, such as that from #740.

const int MagicId = 37;
var sourceCache = new SourceCache<Person, int>(p => p.Id);

using var cleanup1 = sourceCache.ToOptionalObservable(MagicId , initialOptionalWhenMissing: true)
                        .OnHasNoValue(() => Console.WriteLine("Person is not present"))
                        .Convert(p => p.FullName)
                        .SelectValues()
                        .Subscribe(name => Console.WriteLine("Person's Full Name: " + name));

using var cleanup2 = sourceCache.ToOptionalObservable(MagicId , initialOptionalWhenMissing: false)
                        .OnHasValue(p => Console.WriteLine("Person Added: " + p.FullName))
                        .ValueOrThrow(() => new Exception("Person was removed!"))
                        .Subscribe();

It can also be used with the extension methods added in #739 to create this advanced helper functions that syncs a value between an observable cache and a source cache:

(There are better ways to implement such a thing, this is just an example.)

IDisposable SyncValue<TSource, TKey, TDest, TDestKey>(IObservableCache<TSource, TKey> source, ISourceCache<TDest, TDestKey> destination, TKey syncValueKey, Func<TSource, TDest> converter) =>
    source.Connect()
        .ToOptionalObservable(syncValueKey)  // Create Observable Optional
        .Convert(converter)                  // Convert to Destination Type
        .EditDiff(destination.KeySelector)   // Convert to Change Set
        .PopulateInto(destination);          // Merge into Destination

[codecov]

Codecov Report

Merging #741 (3005431) into main (61900ef) will decrease coverage by 8.19%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #741      +/-   ##
==========================================
- Coverage   72.48%   64.29%   -8.19%     
==========================================
  Files         221      222       +1     
  Lines       11176    11224      +48     
  Branches        0     2271    +2271     
==========================================
- Hits         8101     7217     -884     
+ Misses       3075     3062      -13     
- Partials        0      945     +945     

Files	Coverage Δ
...c/DynamicData/Kernel/OptionObservableExtensions.cs	100.00% <100.00%> (ø)

... and 142 files with indirect coverage changes

[JakenVeina]

All tests are passing on both dwcullop:feature/observable-optional-extensions' and reactivemarbles:main, but dwcullop:feature/observable-optional-extensions' is five commits out-of-date from reactivemarbles:main. I don't know what kinda conflicts ought to be introduced from you only adding files, but that's where the failures have to be coming from, conflicts that the auto-merge isn't smart enough to resolve correctly. Either run a merge from to dwcullop:feature/observable-optional-extensions', or re-base dwcullop:feature/observable-optional-extensions' into reactivemarbles:main to resolve whatever conflicts are causing the failures.

[dwcullop]

Thanks for looking at this.

I think it is up to date. 2 days ago I updated it. I tried to sync again just now and it already has all the commits. This branch is 5 commits ahead, but that's what I'm trying to merge.

The issue isn't a merge conflict. It is saying the coverage level of the unit tests drops below an acceptable level, which is odd because the one file I'm adding has 100% coverage.

[RolandPheasant]

The issue isn't a merge conflict. It is saying the coverage level of the unit tests drops below an acceptable level, which is odd because the one file I'm adding has 100% coverage.

This is odd and looks like the code coverage tool is confused.

[glennawatson]

Codecov recently had an upgrade to its algorithm so suspect it is that. If you check it in it'll just be at that level.

[JakenVeina]

Thanks for looking at this.

I think it is up to date. 2 days ago I updated it. I tried to sync again just now and it already has all the commits. This branch is 5 commits ahead, but that's what I'm trying to merge.

The issue isn't a merge conflict. It is saying the coverage level of the unit tests drops below an acceptable level, which is odd because the one file I'm adding has 100% coverage.

Ah, my mistake, I misread it. Test coverage, not test results.

[github-actions]

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