From 52b5459a0ba6a14e9eea43e565412290eb8f3ceb Mon Sep 17 00:00:00 2001
From: Ruben Schmidmeister <4602612+bash@users.noreply.github.com>
Date: Wed, 17 May 2023 10:50:22 +0200
Subject: [PATCH] Add Discard

Co-Authored-By: Thomas Bruderer <apophis@apophis.ch>
---
 Funcky/Discard.cs            | 19 +++++++++++++++++++
 Funcky/PublicAPI.Shipped.txt |  2 ++
 changelog.md                 | 14 ++++++++++++++
 3 files changed, 35 insertions(+)
 create mode 100644 Funcky/Discard.cs

diff --git a/Funcky/Discard.cs b/Funcky/Discard.cs
new file mode 100644
index 00000000..9899fabd
--- /dev/null
+++ b/Funcky/Discard.cs
@@ -0,0 +1,19 @@
+namespace Funcky;
+
+public static class Discard
+{
+    /// <summary>A convenient shortcut for getting a <see cref="Unit"/>.
+    /// Useful for using switch expressions purely with guards when matching on non-constant values
+    /// or as an alternative to <c>if</c> / <c>else if</c> / <c>else</c> chains.</summary>
+    /// <example><code>
+    /// using static Funcky.Discard;
+    /// return __ switch
+    /// {
+    ///     _ when user.IsFrenchAdmin() => "le sécret",
+    ///     _ when user.IsAdmin() => "secret",
+    ///     _ => "(redacted)",
+    /// };
+    /// </code></example>
+    /// <remarks>The name is intentionally two underscores as to not conflict with C#'s discard syntax.</remarks>
+    public static readonly Unit __ = Unit.Value;
+}
diff --git a/Funcky/PublicAPI.Shipped.txt b/Funcky/PublicAPI.Shipped.txt
index 70c4ba95..919b267b 100644
--- a/Funcky/PublicAPI.Shipped.txt
+++ b/Funcky/PublicAPI.Shipped.txt
@@ -1,4 +1,5 @@
 #nullable enable
+Funcky.Discard
 Funcky.EitherOrBoth
 Funcky.EitherOrBoth<TLeft, TRight>
 Funcky.EitherOrBoth<TLeft, TRight>.EitherOrBoth() -> void
@@ -773,3 +774,4 @@ static Funcky.Unit.operator ==(Funcky.Unit left, Funcky.Unit right) -> bool
 static Funcky.Unit.operator >(Funcky.Unit left, Funcky.Unit right) -> bool
 static Funcky.Unit.operator >=(Funcky.Unit left, Funcky.Unit right) -> bool
 static Funcky.Unit.Value.get -> Funcky.Unit
+static readonly Funcky.Discard.__ -> Funcky.Unit
diff --git a/changelog.md b/changelog.md
index 357048f5..47613ca8 100644
--- a/changelog.md
+++ b/changelog.md
@@ -17,6 +17,20 @@ var greeting = person switch
 record Person(string FirstName, Option<string> LastName);
 ```
 
+### Discard
+The new `Discard.__` field provides a short-hand for `Unit.Value` to be used with `switch` expressions.
+
+```cs
+using static Funcky.Discard;
+
+return __ switch
+{
+    _ when user.IsFrenchAdmin() => "le sécret",
+    _ when user.IsAdmin() => "secret",
+    _ => "(redacted)",
+};
+```
+
 ### Retry with Exception
 We've added overloads to the `Retry` and `RetryAsync` functions that allow retrying a function
 as long as an exception is thrown.