allowing overrides for ShallowEquality

Author: krauthaufen

RELEASE_NOTES.md

@@ -1,3 +1,6 @@
+### 0.0.25
+* allowing overrides for ShallowEquality via `ShallowEquality<'T>.Set(...)`
+
 ### 0.0.24
 * weak callbacks are now correctly GC'ed individually
 * some new IndexList combinators

src/FSharp.Data.Adaptive/ShallowEquality.fs

@@ -13,16 +13,23 @@ module private ShallowEqualityHelpers =
     let inline hash (a : 'a) = (a :> obj).GetHashCode()
 
 type ShallowEqualityComparer<'a> private() =
-    static let instance = ShallowEqualityComparer<'a>() :> System.Collections.Generic.IEqualityComparer<'a>
+    static let mutable instance = 
+        { new System.Collections.Generic.IEqualityComparer<'a> with
+            member x.GetHashCode v = ShallowEqualityHelpers.hash v
+            member x.Equals(a,b) = ShallowEqualityHelpers.equals a b
+        }
 
     static member Instance = instance
+    
+    static member Set(newInstance : System.Collections.Generic.IEqualityComparer<'a>) =
+        instance <- newInstance
 
-    static member ShallowHashCode v = ShallowEqualityHelpers.hash v
-    static member ShallowEquals(a,b) = ShallowEqualityHelpers.equals a b
+    static member ShallowHashCode v = instance.GetHashCode v
+    static member ShallowEquals(a,b) = instance.Equals(a,b)
 
     interface System.Collections.Generic.IEqualityComparer<'a> with
-        member x.GetHashCode v = ShallowEqualityHelpers.hash v
-        member x.Equals(a,b) = ShallowEqualityHelpers.equals a b
+        member x.GetHashCode v = instance.GetHashCode v
+        member x.Equals(a,b) = instance.Equals(a,b)
 
 #else
 open System.Reflection.Emit
@@ -172,15 +179,22 @@ type ShallowEqualityComparer<'a> private() =
         else
             fun (a : 'a) (b : 'a) -> System.Object.ReferenceEquals(a :> obj, b :> obj)
 
-    static let instance = ShallowEqualityComparer<'a>() :> System.Collections.Generic.IEqualityComparer<'a>
+    static let mutable instance = 
+        { new System.Collections.Generic.IEqualityComparer<'a> with
+            member x.GetHashCode v = getHashCode v
+            member x.Equals(a,b) = equals a b
+        }
 
     static member Instance = instance
 
-    static member ShallowHashCode v = getHashCode v
-    static member ShallowEquals(a,b) = equals a b
+    static member Set(newInstance : System.Collections.Generic.IEqualityComparer<'a>) =
+        instance <- newInstance
+
+    static member ShallowHashCode v = instance.GetHashCode v
+    static member ShallowEquals(a,b) = instance.Equals(a,b)
 
     interface System.Collections.Generic.IEqualityComparer<'a> with
-        member x.GetHashCode v = getHashCode v
-        member x.Equals(a,b) = equals a b
+        member x.GetHashCode v = instance.GetHashCode v
+        member x.Equals(a,b) = instance.Equals(a,b)
 
 #endif

src/FSharp.Data.Adaptive/Utilities/Utilities.fs

@@ -123,11 +123,11 @@ module internal CheapEquality =
     open System.Runtime.CompilerServices
 
     #if FABLE_COMPILER
-    let cheapHash (a : 'T) = ShallowEqualityComparer<'T>.ShallowHashCode a
-    let cheapEqual (a : 'T) (b : 'T) = ShallowEqualityComparer<'T>.ShallowEquals(a, b)
+    let cheapHash (a : 'T) = ShallowEqualityComparer<'T>.Instance.GetHashCode a
+    let cheapEqual (a : 'T) (b : 'T) = ShallowEqualityComparer<'T>.Instance.Equals(a, b)
     #else
-    let cheapHash (a : 'T) = ShallowEqualityComparer<'T>.ShallowHashCode a
-    let cheapEqual (a : 'T) (b : 'T) = ShallowEqualityComparer<'T>.ShallowEquals(a, b)
+    let cheapHash (a : 'T) = ShallowEqualityComparer<'T>.Instance.GetHashCode a
+    let cheapEqual (a : 'T) (b : 'T) = ShallowEqualityComparer<'T>.Instance.Equals(a, b)
     #endif 
 
 module internal Unchecked =