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