Merge pull request #741 from polyadic/to-async-enumerable

Add `ToAsyncEnumerable` extension for `Option`

Funcky.Async.Test/Monads/OptionAsyncExtensions/ToAsyncEnumerableTest.cs

@@ -0,0 +1,19 @@
+namespace Funcky.Async.Test.Monads.OptionAsyncExtensions;
+
+public sealed class ToAsyncEnumerableTest
+{
+    [Fact]
+    public async Task ReturnsEmptyEnumerableWhenOptionIsEmpty()
+    {
+        var option = Option<int>.None;
+        Assert.True(await option.ToAsyncEnumerable().NoneAsync());
+    }
+
+    [Fact]
+    public async Task ReturnsEnumerableWithOneElementWhenOptionHasValue()
+    {
+        const int value = 42;
+        var option = Option.Some(value);
+        Assert.Equal(value, await option.ToAsyncEnumerable().SingleAsync());
+    }
+}

Funcky.Async/Monads/Option/OptionExtensions.ToAsyncEnumerable.cs

@@ -0,0 +1,14 @@
+namespace Funcky.Monads;
+
+public static partial class OptionAsyncExtensions
+{
+    /// <summary>
+    /// Returns an <see cref="IAsyncEnumerable{T}"/> that yields exactly one value when the option
+    /// has an item and nothing when the option is empty.
+    /// </summary>
+    public static IAsyncEnumerable<TItem> ToAsyncEnumerable<TItem>(this Option<TItem> option)
+        where TItem : notnull
+        => option.Match(
+            none: AsyncEnumerable.Empty<TItem>,
+            some: AsyncSequence.Return);
+}

Funcky.Async/PublicAPI.Unshipped.txt

@@ -1 +1,2 @@
 #nullable enable
+static Funcky.Monads.OptionAsyncExtensions.ToAsyncEnumerable<TItem>(this Funcky.Monads.Option<TItem> option) -> System.Collections.Generic.IAsyncEnumerable<TItem>!