Add initial project structure with Result type and extension methods

Rehlert.RoP/Extensions/OnErrorExtensions.cs

@@ -0,0 +1,55 @@
+namespace Rehlert.RoP.Extensions;
+
+public static class OnErrorExtensions
+{
+    public static Result<TIn, TErr> OnError<TIn, TErr>(this Result<TIn, TErr> value, Action<TErr> action)
+    {
+        value.Match(
+            _ => { },
+            err => action(err.Value)
+        );
+
+        return value;
+    }
+
+    public static async Task<Result<TIn, TErr>> OnError<TIn, TErr>(
+        this Result<TIn, TErr> value,
+        Func<TErr, Task> func
+    )
+    {
+        await value.Match(
+            _ => Task.CompletedTask,
+            err => func(err.Value)
+        );
+
+        return value;
+    }
+
+    public static async Task<Result<TIn, TErr>> OnError<TIn, TErr>(
+        this Task<Result<TIn, TErr>> value,
+        Func<TErr, Task> func
+    )
+    {
+        var valRes = await value;
+        await valRes.Match(
+            _ => Task.CompletedTask,
+            err => func(err.Value)
+        );
+
+        return valRes;
+    }
+
+    public static async Task<Result<TIn, TErr>> OnError<TIn, TErr>(
+        this Task<Result<TIn, TErr>> value,
+        Action<TErr> action
+    )
+    {
+        var valRes = await value;
+        valRes.Match(
+            _ => { },
+            err => action(err.Value)
+        );
+
+        return valRes;
+    }
+}