From a56a4ff5f2bdb71fcf6d355ba44b59cbe5ffd7f2 Mon Sep 17 00:00:00 2001
From: Kyle Ratti <kyleratti@users.noreply.github.com>
Date: Wed, 7 Feb 2024 20:57:33 -0500
Subject: [PATCH] fix: handle nullable value types in Maybe.Cast

---
 Base.Tests/Structures/MaybeTests.cs | 58 +++++++++++++++++++++++++++++
 Base/Structures/Maybe.cs            |  9 ++++-
 2 files changed, 66 insertions(+), 1 deletion(-)

diff --git a/Base.Tests/Structures/MaybeTests.cs b/Base.Tests/Structures/MaybeTests.cs
index 3a377c6..ea13305 100644
--- a/Base.Tests/Structures/MaybeTests.cs
+++ b/Base.Tests/Structures/MaybeTests.cs
@@ -90,4 +90,62 @@ public class MaybeTests
 		Assert.That(result.HasValue, Is.True);
 		Assert.That(result.Value, Is.EqualTo(30));
 	}
+
+	[Test]
+	public void Cast_ToNullableReferenceType_ReturnsEmptyMaybe_WhenHasNoValue()
+	{
+		// Arrange
+		var maybe = Maybe.Empty<string>();
+
+		// Act
+		var result = maybe.Cast<string?>();
+
+		// Assert
+		Assert.That(result, Is.InstanceOf<Maybe<string?>>());
+		Assert.That(result.HasValue, Is.False);
+	}
+
+	[Test]
+	public void Cast_ToNullableReferenceType_ReturnsMaybe_WhenHasValue()
+	{
+		// Arrange
+		var maybe = Maybe.Just("banana");
+
+		// Act
+		var result = maybe.Cast<string?>();
+
+		// Assert
+		Assert.That(result, Is.InstanceOf<Maybe<string?>>());
+		Assert.That(result.HasValue, Is.True);
+		Assert.That(result.Value, Is.EqualTo("banana"));
+	}
+
+	[Test]
+	public void Cast_ToNullableValueType_ReturnsEmptyMaybe_WhenHasNoValue()
+	{
+		// Arrange
+		var maybe = Maybe.Empty<int>();
+
+		// Act
+		var result = maybe.Cast<string?>();
+
+		// Assert
+		Assert.That(result, Is.InstanceOf<Maybe<string?>>());
+		Assert.That(result.HasValue, Is.False);
+	}
+
+	[Test]
+	public void Cast_ToNullableValueType_ReturnsMaybe_WhenHasValue()
+	{
+		// Arrange
+		var maybe = Maybe.Just(25);
+
+		// Act
+		var result = maybe.Cast<int?>();
+
+		// Assert
+		Assert.That(result, Is.InstanceOf<Maybe<int?>>());
+		Assert.That(result.HasValue, Is.True);
+		Assert.That(result.Value, Is.EqualTo(25));
+	}
 }
diff --git a/Base/Structures/Maybe.cs b/Base/Structures/Maybe.cs
index 6d06d0e..39b2eca 100644
--- a/Base/Structures/Maybe.cs
+++ b/Base/Structures/Maybe.cs
@@ -70,7 +70,14 @@ public readonly struct Maybe<T>
 
 		try
 		{
-			return (TOutput)Convert.ChangeType(Value, typeof(TOutput))!;
+			var t = typeof(TOutput);
+			t = Nullable.GetUnderlyingType(t) ?? t;
+
+			var output = Value == null
+				? default
+				: (TOutput)Convert.ChangeType(Value, t);
+
+			return Maybe.Just(output, hasValue: _ => output != null)!;
 		}
 		catch (InvalidCastException)
 		{