+ HashSet operations

Author: gusty

src/FSharpPlus/Control/Monoid.fs

@@ -29,6 +29,7 @@ type Plus =
     static member        ``+`` (x: Set<_>            , y                    , [<Optional>]_mthd: Plus    ) = Set.union x y
 
     #if !FABLE_COMPILER
+    static member        ``+`` (x: HashSet<_>        , y                    , [<Optional>]_mthd: Plus    ) = HashSet.union x y
     static member        ``+`` (x: StringBuilder     , y: StringBuilder     , [<Optional>]_mthd: Plus    ) = StringBuilder().Append(x).Append(y)
     static member        ``+`` (_: Id0               , _: Id0               , [<Optional>]_mthd: Plus    ) = Id0 ""    
     static member        ``+`` (x: AggregateException, y: AggregateException, [<Optional>]_mthd: Plus    ) = Exception.add x y

src/FSharpPlus/Control/Numeric.fs

@@ -6,6 +6,7 @@ namespace FSharpPlus.Control
 
 open System.Runtime.InteropServices
 open FSharpPlus.Internals
+open FSharpPlus
 #if FABLE_COMPILER
 /// NOTE
 type OptionalAttribute ()=
@@ -143,6 +144,7 @@ type Zero =
     static member        Zero (_: unit                           , _: Zero    ) = ()
     static member        Zero (_: bool                           , _: Zero    ) = false
     static member        Zero (_: Set<'a>                        , _: Zero    ) = Set.empty : Set<'a>
+    static member        Zero (_: HashSet<'a>                    , _: Zero    ) = HashSet.empty : HashSet<'a>
     static member        Zero (_: Map<'a,'b>                     , _: Zero    ) = Map.empty : Map<'a,'b>
 
     static member inline Invoke () =
@@ -213,7 +215,7 @@ type Zero with
     static member inline Zero (_: ^R                             , _: Default5) = Implicit.Invoke 0   : ^R
 
     static member        Zero (_: seq<'a>                        , _: Default4) = Seq.empty      : seq<'a>
-    static member        Zero (_: IEnumerator<'a>                , _: Default4) = FSharpPlus.Enumerator.Empty () : IEnumerator<'a>
+    static member        Zero (_: IEnumerator<'a>                , _: Default4) = Enumerator.Empty () : IEnumerator<'a>
     static member        Zero (_: IDictionary<'a,'b>             , _: Default4) = Dictionary<'a,'b> () :> IDictionary<'a,'b>
     static member        Zero (_: IReadOnlyDictionary<'a,'b>     , _: Default4) = Dictionary<'a,'b> () :> IReadOnlyDictionary<'a,'b>
     static member inline Zero (_: 't                             , _: Default3) = (^t : (static member Empty: ^t) ()) : 't

src/FSharpPlus/Extensions/HashSet.fs

@@ -0,0 +1,43 @@
+namespace FSharpPlus
+
+/// Additional operations on HashSet<'T>
+[<RequireQualifiedAccess>]
+module HashSet =
+    open System.Collections.Generic
+    open System.Collections.ObjectModel
+
+
+    /// <summary>The empty set for the type 'T.</summary>
+    [<GeneralizableValue>]
+    [<CompiledName("Empty")>]
+    let empty<'T> : HashSet<'T> = HashSet<'T> ()
+
+    /// <summary>The set containing the given element.</summary>
+    /// <param name="value">The value for the set to contain.</param>
+    /// <returns>The set containing <c>value</c>.</returns>
+    [<CompiledName("Singleton")>]
+    let singleton (value: 'T) : HashSet<'T> =
+        let set =
+            #if FABLE_COMPILER
+            HashSet<'T> ()
+            #else
+            HashSet<'T> 1
+            #endif
+        set.Add value |> ignore
+        set
+
+    /// <summary>Computes the union of the two sets.</summary>
+    /// <param name="set1">The first input set.</param>
+    /// <param name="set2">The second input set.</param>
+    /// <returns>The union of <c>set1</c> and <c>set2</c>.</returns>
+    [<CompiledName("Union")>]
+    let union (x: HashSet<'T>) (y: HashSet<'T>) : HashSet<'T> =
+        let union =
+            #if FABLE_COMPILER
+            HashSet<'T> ()
+            #else
+            HashSet<'T> (max x.Count y.Count)
+            #endif
+        for item in x do union.Add item |> ignore
+        for item in y do union.Add item |> ignore
+        union

src/FSharpPlus/FSharpPlus.fsproj

@@ -50,6 +50,7 @@
     <Compile Include="Extensions/Map.fs" />
     <Compile Include="Extensions/Dictionary.fs" />
     <Compile Include="Extensions/Dict.fs" />
+    <Compile Include="Extensions/HashSet.fs" />
     <Compile Include="Extensions/IReadOnlyDictionary.fs" />
     <Compile Include="Extensions/Enumerator.fs" />
     <Compile Include="Extensions/Task.fs" />