Fix lazy views (#7)

* use hash of IStructuralEquatable using the default comparer

* use way simpler implementation

* simplify view caching

Author: JaggerJo

src/Avalonia.FuncUI.UnitTests/LibTests.fs

@@ -3,24 +3,20 @@
 open Xunit
 open System
 
-module LibTests =
-    module FuncTests = 
-        open Avalonia.FuncUI.Lib
+module Library =
 
-        type Msg = Increment | Decrement
+    [<Fact>]
+    let ``fun`` () =
+        
+        let view () =
+            let add = fun (count: int) -> count + 1
+            let sub = fun (count: int) -> count - 1
+            (add, sub)
 
-        type State = { count : int }
+        let (add', sub') = view ()
+        let (add'', sub'') = view ()
 
-        [<Fact>]
-        let ``Comparing funcs`` () =
-
-            let a = fun (state: State, dispatch: Msg -> unit) -> dispatch Increment
-            let b = fun (state: State, dispatch: Msg -> unit) -> dispatch Increment
-            let c = fun (state: State, dispatch: Msg -> unit) -> dispatch Decrement
-            let d = fun (state: State, dispatch: Msg -> unit) -> a(state, dispatch)
-
-            Assert.True(Func.compare a b)
-            Assert.False(Func.compare a c)
-            Assert.True(Func.isComparable a)
-            Assert.True(Func.isComparable b)
-            Assert.False(Func.isComparable d)
+        Assert.Equal(add'.GetType(), add''.GetType())
+        Assert.Equal(sub'.GetType(), sub''.GetType())
+        Assert.NotEqual(add'.GetType(), sub'.GetType())
+        Assert.NotEqual(add''.GetType(), sub''.GetType())

src/Avalonia.FuncUI/Core/Lib.fs

@@ -1,45 +1,8 @@
 namespace Avalonia.FuncUI.Lib
 
-[<RequireQualifiedAccess>]
-module Func =
-    open System
-
-    (* get IL of method body *)
-    let private getIL (func: 'a -> 'b) =
-        let t = func.GetType()
-        let m = t.GetMethod("Invoke")
-        let b = m.GetMethodBody()
-        b.GetILAsByteArray()
-
-    (* check if func is comparable *)
-    let isComparable(func: 'a -> 'b) =
-        let funcType = func.GetType()
-
-        let hasFields = funcType.GetFields()
-      
-        if funcType.IsGenericType || not (Seq.isEmpty hasFields) then
-            false
-        else
-            true
-
-    (* compares two functions for equality *)
-    let compare (funcA: 'a -> 'b) (funcB: 'c -> 'd) : bool=
-        if not (isComparable funcA) then
-            raise (Exception("function 'funcA' is generic or has outer dependencies"))
-
-        if not (isComparable funcB) then
-            raise (Exception("function 'funcB' is generic or has outer dependencies"))
-
-        let bytesA = getIL funcA
-        let bytesB = getIL funcB
-        let spanA = ReadOnlySpan(bytesA)
-        let spanB = ReadOnlySpan(bytesB)
-        spanA.SequenceEqual(spanB)
-
-    (* get hash of method body *)
-    let hashMethodBody (func: 'a -> 'b) : int =
-        let bytes = (getIL func) :> System.Collections.IStructuralEquatable
-        bytes.GetHashCode()
+type MutableList<'t> = System.Collections.Generic.List<'t>
+type MutableDict<'key, 'value> = System.Collections.Generic.Dictionary<'key, 'value>
+type CuncurrentDict<'key, 'value> = System.Collections.Concurrent.ConcurrentDictionary<'key, 'value>
 
 module Reflection =
     open System.Reflection

src/Avalonia.FuncUI/DSL.base.fs

@@ -1,10 +1,8 @@
 namespace rec Avalonia.FuncUI
 
-open Avalonia.Controls
 open System
 open Types
 open Avalonia.FuncUI.Lib
-open Types
 
 type TypedAttr<'t> =
     | Property of PropertyAttr
@@ -14,10 +12,11 @@ type TypedAttr<'t> =
     | Lifecycle of LifecylceAttr
 
 [<AbstractClass; Sealed>]
-type Views private () =
+type Views () =
+
+    static let cache = CuncurrentDict<int, View>()
 
-    // TODO: Check if using a mutable hash map makes a big difference
-    static let cache = ref Map.empty
+    static member val CacheMaxLength : int = 1000 with get, set
 
     (* create view - intended for internal use *)
     static member create<'t>(attrs: TypedAttr<'t> list) : View =
@@ -33,18 +32,25 @@ type Views private () =
         { ViewType = typeof<'t>; Attrs = mappedAttrs; }
 
     (* lazy views with caching *)
-    static member viewLazy (state: 'state) (dispatch: 'dispatch) (func: 'state -> 'dispatch -> View) : View =
-        let hash (state: 'state, func: 'state -> 'dispatch -> View) : int =
-            Tuple(state, Func.hashMethodBody func).GetHashCode()
-
-        let key = hash(state, func)
-
-        match (!cache).TryFind key with
-        | Some cached -> cached
-        | None ->
-            let computedValue = func state dispatch
-            cache := (!cache).Add (key, computedValue)
-            computedValue
+    static member viewLazy (state: 'state, args: 'args, func: 'state -> 'args -> View) : View =
+
+        let key = Tuple(state, func.GetType()).GetHashCode()
+
+        if (cache.Count >= Views.CacheMaxLength) then
+            cache.Clear()
+
+        printfn "cache length is %i" cache.Count
+
+        let hasValue, value = cache.TryGetValue key
+
+        match hasValue with
+        | true -> value
+        | false ->
+            cache.AddOrUpdate(
+                key,
+                (fun _ -> func state args),
+                (fun _ _ -> func state args)
+            )
 
 
 [<AbstractClass; Sealed>]