Add Obj module (#663)

Author: gusty

src/FSharpPlus/Extensions/Obj.fs

@@ -0,0 +1,36 @@
+namespace FSharpPlus
+
+/// Additional operations on (reference) objects
+[<RequireQualifiedAccess>]
+module Obj =
+
+    /// <summary>Returns the source if it is not null; otherwise, returns the specified default value.</summary>
+    /// <param name="value">The default value to return if the source is null.</param>
+    /// <param name="source">The source object.</param>
+    /// <returns>The source if it is not null; otherwise, the specified default value.</returns>
+    /// <remarks>The default value is evaluated eagerly.</remarks>
+    let defaultValue value (source: 'T) : 'T =
+        match source with
+        | null  -> value
+        | value -> value
+
+    /// <summary>Returns the source if it is not null; otherwise, invokes the specified function to obtain a default value.</summary>
+    /// <param name="fNull">The function to invoke to obtain a default value if the source is null.</param>
+    /// <param name="source">The source object.</param>
+    /// <returns>The source if it is not null; otherwise, the result of invoking the specified function.</returns>
+    /// <remarks>The fNull function is only invoked if the source is null.</remarks>
+    let inline defaultWith ([<InlineIfLambda>]fNull: unit -> 'T) (source: 'T) : 'T =
+        match source with
+        | null -> fNull ()
+        | value -> value
+
+    /// <summary>Applies one of two functions to the source object based on whether it is null or not.</summary>
+    /// <param name="fValue">The function to apply if the source is not null.</param>
+    /// <param name="fNull">The function to apply if the source is null.</param>
+    /// <param name="source">The source object.</param>
+    /// <returns>The result of applying fValue to the source if it is not null; otherwise, the result of applying fNull.</returns>
+    /// <remarks>Only one of the functions is invoked based on the nullity of the source.</remarks>
+    let inline either ([<InlineIfLambda>]fValue: 'T -> 'U) ([<InlineIfLambda>]fNull: unit -> 'U) (source: 'T) : 'U =
+        match source with
+        | null  -> fNull ()
+        | value -> fValue value

src/FSharpPlus/FSharpPlus.fsproj

@@ -34,6 +34,7 @@
     <Compile Include="Internals.fs" />
     <Compile Include="Extensions/Option.fs" />
     <Compile Include="Extensions/ValueOption.fs" />
+    <Compile Include="Extensions/Obj.fs" />
     <Compile Include="Extensions/Nullable.fs" />
     <Compile Include="Extensions/Result.fs" />
     <Compile Include="Extensions/Choice.fs" />