Daily Perf Improver: Optimize memory allocations in JSON type providers

src/FSharp.Data.Json.Core/JsonDocument.fs

@@ -91,7 +91,22 @@ type JsonDocument =
         use reader = reader
         let text = reader.ReadToEnd()
 
-        match JsonValue.ParseMultiple(text) |> Seq.toArray with
-        | [| JsonValue.Array array |] -> array
-        | array -> array
-        |> Array.mapi (fun i value -> JsonDocument.Create(value, "[" + (string i) + "]"))
+        // Optimization: Process parsed values more efficiently to reduce allocations
+        let parsedSequence = JsonValue.ParseMultiple(text)
+
+        // Convert to array only once and handle the special case efficiently
+        let parsedArray = parsedSequence |> Seq.toArray
+
+        let valuesArray =
+            match parsedArray with
+            | [| JsonValue.Array array |] -> array
+            | array -> array
+
+        // Optimization: Pre-allocate result array instead of using Array.mapi
+        // This avoids creating intermediate mapping functions and reduces allocations
+        let resultArray = Array.zeroCreate<IJsonDocument> valuesArray.Length
+
+        for i = 0 to valuesArray.Length - 1 do
+            resultArray.[i] <- JsonDocument.Create(valuesArray.[i], "[" + (string i) + "]")
+
+        resultArray

src/FSharp.Data.Json.Core/JsonRuntime.fs

@@ -93,12 +93,19 @@ type JsonRuntime =
     static member ConvertArray<'T>(doc: IJsonDocument, mapping: Func<IJsonDocument, 'T>) =
         match doc.JsonValue with
         | JsonValue.Array elements ->
-            elements
-            |> Array.filter (function
-                | JsonValue.Null -> false
-                | JsonValue.String s when s |> TextConversions.AsString |> Option.isNone -> false
-                | _ -> true)
-            |> Array.mapi (fun i value -> doc.CreateNew(value, "[" + (string i) + "]") |> mapping.Invoke)
+            // Optimization: Filter and map in single pass to reduce array allocations
+            let result = ResizeArray<'T>()
+            let mutable index = 0
+
+            for value in elements do
+                match value with
+                | JsonValue.Null -> ()
+                | JsonValue.String s when s |> TextConversions.AsString |> Option.isNone -> ()
+                | _ ->
+                    result.Add(doc.CreateNew(value, "[" + (string index) + "]") |> mapping.Invoke)
+                    index <- index + 1
+
+            result.ToArray()
         | JsonValue.Null -> [||]
         | x ->
             failwithf "Expecting an array at '%s', got %s" (doc.Path())
@@ -247,9 +254,17 @@ type JsonRuntime =
         =
         match doc.JsonValue with
         | JsonValue.Array elements ->
-            elements
-            |> Array.filter (JsonRuntime.Matches cultureStr (InferedTypeTag.ParseCode tagCode))
-            |> Array.mapi (fun i value -> doc.CreateNew(value, "[" + (string i) + "]") |> mapping.Invoke)
+            // Optimization: Filter and map in single pass to reduce array allocations
+            let result = ResizeArray<'T>()
+            let mutable index = 0
+            let matchFunc = JsonRuntime.Matches cultureStr (InferedTypeTag.ParseCode tagCode)
+
+            for value in elements do
+                if matchFunc value then
+                    result.Add(doc.CreateNew(value, "[" + (string index) + "]") |> mapping.Invoke)
+                    index <- index + 1
+
+            result.ToArray()
         | JsonValue.Null -> [||]
         | x ->
             failwithf "Expecting an array at '%s', got %s" (doc.Path())