Change StartPosition type from an alias to a DU to avoid mistakes

Author: Jamil Maqdis Anton

src/Read.fs

@@ -10,20 +10,30 @@ module Read =
         | ReadVersion.End -> int (Position.End)
         | ReadVersion.SpecificVersion version -> int (version)
 
-    let readFromAllStream: SqlStreamStore.IStreamStore -> ReadingDirection -> StartPositionInclusive -> MessageCount -> Async<ReadAllPage> =
+    let private fromStartPositionInclusive: StartPosition -> int64 =
+        function
+        | StartPosition.Start -> 0L
+        | StartPosition.End -> -1L
+        | StartPosition.SpecificPosition position -> position
+
+    let readFromAllStream: SqlStreamStore.IStreamStore -> ReadingDirection -> StartPosition -> MessageCount -> Async<ReadAllPage> =
         fun store readingDirection startPositionInclusive msgCount ->
             match readingDirection with
-            | ReadingDirection.Forward -> store.ReadAllForwards(startPositionInclusive, msgCount)
-            | ReadingDirection.Backward -> store.ReadAllBackwards(startPositionInclusive, msgCount)
+            | ReadingDirection.Forward ->
+                store.ReadAllForwards(fromStartPositionInclusive startPositionInclusive, msgCount)
+            | ReadingDirection.Backward ->
+                store.ReadAllBackwards(fromStartPositionInclusive startPositionInclusive, msgCount)
             |> Async.AwaitTask
 
-    let readFromAllStream': SqlStreamStore.IStreamStore -> ReadingDirection -> StartPositionInclusive -> MessageCount -> bool -> CancellationToken -> Async<ReadAllPage> =
+    let readFromAllStream': SqlStreamStore.IStreamStore -> ReadingDirection -> StartPosition -> MessageCount -> bool -> CancellationToken -> Async<ReadAllPage> =
         fun store readingDirection startPositionInclusive msgCount prefetchJson cancellationToken ->
             match readingDirection with
             | ReadingDirection.Forward ->
-                store.ReadAllForwards(startPositionInclusive, msgCount, prefetchJson, cancellationToken)
+                store.ReadAllForwards
+                    (fromStartPositionInclusive startPositionInclusive, msgCount, prefetchJson, cancellationToken)
             | ReadingDirection.Backward ->
-                store.ReadAllBackwards(startPositionInclusive, msgCount, prefetchJson, cancellationToken)
+                store.ReadAllBackwards
+                    (fromStartPositionInclusive startPositionInclusive, msgCount, prefetchJson, cancellationToken)
             |> Async.AwaitTask
 
     let readFromStream: SqlStreamStore.IStreamStore -> ReadingDirection -> StreamName -> ReadVersion -> MessageCount -> Async<ReadStreamPage> =

src/Types.fs

@@ -15,9 +15,9 @@ type StreamName = string
 
 [<RequireQualifiedAccessAttribute>]
 type ReadVersion =
-     | Start
-     | End
-     | SpecificVersion of uint
+    | Start
+    | End
+    | SpecificVersion of uint
 
 [<RequireQualifiedAccessAttribute>]
 type AppendVersion =
@@ -26,7 +26,12 @@ type AppendVersion =
     | NoStream
     | SpecificVersion of int
 
-type StartPositionInclusive = int64
+[<RequireQualifiedAccessAttribute>]
+type StartPosition =
+    | Start
+    | End
+    | SpecificPosition of int64
+
 type MessageCount = int
 
 [<RequireQualifiedAccessAttribute>]