From 238814edbb5538bc3a0d8189a09dd842210042dd Mon Sep 17 00:00:00 2001
From: Oli Sturm <oliver@oliversturm.com>
Date: Wed, 5 Oct 2022 11:51:55 +0100
Subject: [PATCH] adding CS11 list patterns

---
 samples/CS11/CS11.csproj | 10 ++++++++
 samples/CS11/Program.cs  | 49 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)
 create mode 100644 samples/CS11/CS11.csproj
 create mode 100644 samples/CS11/Program.cs

diff --git a/samples/CS11/CS11.csproj b/samples/CS11/CS11.csproj
new file mode 100644
index 0000000..d439800
--- /dev/null
+++ b/samples/CS11/CS11.csproj
@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>
diff --git a/samples/CS11/Program.cs b/samples/CS11/Program.cs
new file mode 100644
index 0000000..50afaed
--- /dev/null
+++ b/samples/CS11/Program.cs
@@ -0,0 +1,49 @@
+namespace CS11 {
+  class Program {
+    static void Main(string[] args) {
+      int[] numbers = { 1, 3, 42 };
+      // Exact match
+      Console.WriteLine($"numbers is [1,3,42]: {numbers is [1, 3, 42]}");
+      // Must be correct length, so this is false
+      Console.WriteLine($"numbers is [1,3]: {numbers is [1, 3]}");
+      // Can use wildcards
+      Console.WriteLine($"numbers is [1,3,_]: {numbers is [1, 3, _]}");
+      // Still must be correct length!
+      Console.WriteLine($"numbers is [1,3,_,_]: {numbers is [1, 3, _, _]}");
+
+      // Really don't care about length? Use ..
+      Console.WriteLine($"numbers is [..,42]: {numbers is [.., 42]}");
+
+      // Cool stuff, match with embedded patterns - this is true
+      Console.WriteLine($"numbers is [1,3,>10]: {numbers is [1, 3, > 10]}");
+      // ... and this is false
+      Console.WriteLine($"numbers is [1,3,>100]: {numbers is [1, 3, > 100]}");
+
+
+      // Docs at https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/patterns#list-patterns
+      // show an example with CSV import -- cool idea, but of course
+      // the CSV content is always a list of strings so advanced
+      // patterns can't be used for non-string content.
+
+      // What the docs don't tell you (at least I didn't see it
+      // anywhere -- found it in GitHub), you can split head and tail
+      // On second read, I found this:
+      // "The var pattern can capture a single element, or a range of elements."
+      // I imagine that somebody thought this would be sufficient.
+      if (numbers is [var x, .. var xs]) {
+        Console.WriteLine($"Head: {x}");
+        Console.WriteLine($"Tail: {xs}");
+      }
+
+      // So we can do nice functional-style stuff:
+      Console.WriteLine($"Sum of numbers: {Sum(numbers)}");
+    }
+
+    // Now we're talking
+    static int Sum(int[] l) => l switch
+    {
+      [] => 0,
+      [var x, .. var xs] => x + Sum(xs)
+    };
+  }
+}