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This commit is contained in:
Oli Sturm
2025-05-08 14:17:31 +01:00
parent 768d01a37d
commit c9c1b53630
9 changed files with 143 additions and 16 deletions
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samples/.idea/.idea.samples/.idea/indexLayout.xml
Generated
+3 -1
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@@ -1,7 +1,9 @@
<?xml version="1.0" encoding="UTF-8"?>
<project version="4">
<component name="UserContentModel">
<attachedFolders />
<attachedFolders>
<Path>../../advanced-pattern-matching-cs-samples</Path>
</attachedFolders>
<explicitIncludes />
<explicitExcludes />
</component>
samples/CS11/Program.cs
+97 -9
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@@ -1,25 +1,42 @@
// ReSharper disable All
using System.Text.Json;
namespace CS11 {
class Program {
static void Main(string[] args) {
int[] numbers = { 1, 3, 42 };
// The following match expressions are "slice patterns" - rather unintuitive naming in my eyes, but what can we do.
// Exact match
Console.WriteLine($"numbers is [1,3,42]: {numbers is [1, 3, 42]}");
Console.WriteLine($"numbers is [1, 3, 42]: {numbers is [1, 3, 42]}");
// Must be correct length, so this is false
Console.WriteLine($"numbers is [1,3]: {numbers is [1, 3]}");
Console.WriteLine($"numbers is [1, 3]: {numbers is [1, 3]}");
// Can use wildcards
Console.WriteLine($"numbers is [1,3,_]: {numbers is [1, 3, _]}");
Console.WriteLine($"numbers is [1, 3, _]: {numbers is [1, 3, _]}");
// Still must be correct length!
Console.WriteLine($"numbers is [1,3,_,_]: {numbers is [1, 3, _, _]}");
Console.WriteLine($"numbers is [1, 3, _, _]: {numbers is [1, 3, _, _]}");
// Really don't care about length? Use ..
Console.WriteLine($"numbers is [..,42]: {numbers is [.., 42]}");
Console.WriteLine($"numbers is [.., 42]: {numbers is [.., 42]}");
// Cool stuff, match with embedded patterns - this is true
Console.WriteLine($"numbers is [1,3,>10]: {numbers is [1, 3, > 10]}");
Console.WriteLine($"numbers is [1, 3, >10]: {numbers is [1, 3, > 10]}");
// ... and this is false
Console.WriteLine($"numbers is [1,3,>100]: {numbers is [1, 3, > 100]}");
Console.WriteLine($"numbers is [1, 3, >100]: {numbers is [1, 3, > 100]}");
// Other combinations possible, this is true
Console.WriteLine($"numbers is [.. , <= 10, >= 10]: {numbers is [.., <= 10, >= 10]}");
// The .. operator can be used in the middle as well. It can also match a zero-length part of the list.
int[] moreNumbers = [10, 20, 30, 40, 50, 60, 70, 80, 90, 100];
Console.WriteLine(
$"moreNumbers is [<= 50, <= 50, .., > 50, >= 100]: {moreNumbers is [<= 50, <= 50, .., > 50, >= 100]}");
Console.WriteLine(
$"numbers is [1, 3, .., 42]: {numbers is [1, 3, .., 42]}");
// Note that .. can be used only once. This is invalid.
// Console.WriteLine(
// $"moreNumbers is [<= 50, <= 50, .., > 50, >= 100]: {moreNumbers is [.., <= 50, <= 50, .., > 50, >= 100]}");
// And one more strange combination:
Console.WriteLine($$"""numbers is [1, .. { Length: 2 }]: {{numbers is [1, .. { Length: 2 }]}}""");
// You can split a list into head and tail:
if (numbers is [var x, .. var xs]) {
@@ -33,20 +50,91 @@ namespace CS11 {
// Talking about spans -- the second new pattern matching feature in
// C# 11 is related to spans and strings.
string WhatsNext(ReadOnlySpan<char> spanString) => spanString switch {
string WhatsNext(ReadOnlySpan<char> spanString) => spanString switch
{
"one" => "two",
"two" => "three",
_ => "That's it!"
};
Console.WriteLine($"One. Next: '{WhatsNext("one".AsSpan())}'");
//----------------------------------------------
//----------------------------------------------
// WE'LL GET BACK TO THIS DEMO IN A LITTLE WHILE
//----------------------------------------------
//----------------------------------------------
//return;
#region FP stuff for the second part of the demo
// Technically, only C# 12 allows collection expressions - we're using them here anyway, for brevity
List<double> values = [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0];
Console.WriteLine($"Downsampled: {JsonSerializer.Serialize(Downsample(values))}");
List<List<int>> m1 = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
Console.WriteLine($"Transpose: {JsonSerializer.Serialize(Transpose(m1))}");
Console.WriteLine($"Transpose: {JsonSerializer.Serialize(Transpose_(m1))}");
#endregion
}
// Now we're talking -- note that the use of Span<T> magically solves
// a perf problem you would have if you used an Array type here.
static int Sum(Span<int> l) => l switch {
static int Sum(Span<int> l) => l switch
{
[] => 0,
[var x, .. var xs] => x + Sum(xs)
};
#region FP stuff for the second part of the demo
// From F#:
// let rec downsample : float list -> float list =
// function
// | [] -> []
// | h1::h2::t -> 0.5 * (h1 + h2) :: downsample t
// | [_] -> invalid_arg "downsample"
static List<double> Downsample(List<double> values) => values switch
{
[var x1, var x2, .. var xs] => new List<double> { (x1 + x2) / 2 }.Concat(Downsample(xs)).ToList(),
_ => []
};
// From F#
// let rec transpose = function
// | (_ :: _) :: _ as xss ->
// List.map List.head xss :: transpose (List.map List.tail xss)
// | _ -> []
static List<List<int>> Transpose(List<List<int>> s) => s switch
{
[[_, .. _], .. _] =>
new List<List<int>> { s.Select(x => x.First()).ToList() }
.Concat<List<int>>(
Transpose(
s.Select(x => x.Skip(1).ToList()).ToList()
)).ToList(),
_ => []
};
// Construction helpers:
static List<R> Map<T, R>(Func<T, R> f, List<T> l) => l.Select(f).ToList();
static T Head<T>(List<T> l) => l[0];
static List<T> Tail<T>(List<T> l) => l.Skip(1).ToList();
static List<T> Cons<T>(T head, List<T> tail) => new List<T> { head }.Concat(tail).ToList();
// Much closer now!
static List<List<int>> Transpose_(List<List<int>> s) => s switch
{
[[_, .. _], .. _] => Cons(Map(Head, s), Transpose_(Map(Tail, s))),
_ => []
};
#endregion
}
}
samples/CS9/Program.cs
+3 -3
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@@ -34,10 +34,11 @@ namespace CS9 {
// Positional patterns with "discard" placeholders - note that
// the element lists must be "complete"!
static OrderValue OrderValueCategory(Order o) =>
o switch {
o switch
{
// Labels are optional here but can be useful
// for readability
(itemCount: < 0, itemPrice: _) => throw new ArgumentException("Positive itemCounts please!"),
Order (itemCount: < 0, itemPrice: _) => throw new ArgumentException("Positive itemCounts please!"),
(_, < 0) => throw new ArgumentException("Positive itemPrices please!"),
(>= 100, _) => OrderValue.ValuableDueToHighCount,
(_, >= 1000) => OrderValue.ValuableDueToHighItemPrice,
@@ -48,7 +49,6 @@ namespace CS9 {
_ => OrderValue.NotValuable
};
static void Main(string[] args) {
}
}
samples/Temp/Program.cs
+20
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@@ -0,0 +1,20 @@
// ReSharper disable InconsistentNaming
namespace Temp;
internal class Program {
private static void Main(string[] args) {
Console.WriteLine("Hello, World!");
}
private (T, U, T, U) BinarySearch<T, U>(Func<T, T, T> Split, Func<T, U> Cmp, (T x, U c_x, T y, U c_y) r) {
T m = Split(r.x, r.y);
U c_m = Cmp(m);
return (r.c_x = c_m, c_m = r.c_y) switch
{
(true, false) => (m, c_m, r.y, r.c_y),
(false, true) => (r.x, r.c_x, m, c_m),
_ => throw new Exception("Not found")
};
}
}
samples/Temp/Temp.csproj
+10
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@@ -0,0 +1,10 @@
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net9.0</TargetFramework>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
</PropertyGroup>
</Project>
samples/fpsamples/sample3.hs
+1 -1
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@@ -9,4 +9,4 @@ fact x | x <= 1 = 1
fact' :: Int -> Int
fact' 0 = 1
fact' 1 = 1
fact' x = x * (fact (x - 1))
fact' x = x * (fact' (x - 1))
samples/fpsamples/sample4.fs
+1
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@@ -12,3 +12,4 @@ let rec listLength l =
let rec listLength' = function
| [] -> 0
| _ :: xs -> 1 + (listLength' xs)
samples/samples.sln
+6
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@@ -13,6 +13,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "CS10", "CS10\CS10.csproj",
EndProject
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "CS11", "CS11\CS11.csproj", "{D1B3E6C4-303A-4A76-B555-4D78E50F8957}"
EndProject
Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Temp", "Temp\Temp.csproj", "{C78DD1B6-35A0-4DAA-85ED-68B06662C523}"
EndProject
Global
GlobalSection(SolutionConfigurationPlatforms) = preSolution
Debug|Any CPU = Debug|Any CPU
@@ -42,5 +44,9 @@ Global
{D1B3E6C4-303A-4A76-B555-4D78E50F8957}.Debug|Any CPU.Build.0 = Debug|Any CPU
{D1B3E6C4-303A-4A76-B555-4D78E50F8957}.Release|Any CPU.ActiveCfg = Release|Any CPU
{D1B3E6C4-303A-4A76-B555-4D78E50F8957}.Release|Any CPU.Build.0 = Release|Any CPU
{C78DD1B6-35A0-4DAA-85ED-68B06662C523}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
{C78DD1B6-35A0-4DAA-85ED-68B06662C523}.Debug|Any CPU.Build.0 = Debug|Any CPU
{C78DD1B6-35A0-4DAA-85ED-68B06662C523}.Release|Any CPU.ActiveCfg = Release|Any CPU
{C78DD1B6-35A0-4DAA-85ED-68B06662C523}.Release|Any CPU.Build.0 = Release|Any CPU
EndGlobalSection
EndGlobal