{"id":429,"date":"2019-06-07T13:13:49","date_gmt":"2019-06-07T03:13:49","guid":{"rendered":"http:\/\/www.nerdhold.com\/coder\/?p=429"},"modified":"2019-06-07T20:39:25","modified_gmt":"2019-06-07T10:39:25","slug":"new-linq-method-torandomcollectiontype","status":"publish","type":"post","link":"http:\/\/www.nerdhold.com\/coder\/2019\/06\/07\/new-linq-method-torandomcollectiontype\/","title":{"rendered":"New LINQ Method: ToRandomCollectionType<>()"},"content":{"rendered":"

If you’ve spent time in the C# world, you’ve probably encountered (and possibly asked) the question: “Should I use .ToList() or .ToArray()?”<\/p>\n

The answer, of course, is that it’s a false dichotomy: I’ve written before about how you should pick the right data structure for the job<\/a>. But what if you really don’t care? What if you’d prefer to just roll the dice and let the computer pick for you? Is that possible?<\/p>\n

Of course it is. First, we need an extension method:<\/p>\n

\r\npublic static class Extensions {\r\n    public static IEnumerable<T> ToRandomCollectionType<T>(this IEnumerable<T> collection) {\r\n        throw new NotImplementedException();\r\n    }\r\n}\r\n<\/pre>\n
The first thing that’s going to have to do is pick a collection type. Let’s load all of the types we can find which implement IEnumerable:<\/p>\n
\r\nvar types = AppDomain.CurrentDomain.GetAssemblies()\r\n                     .SelectMany(assembly => assembly.GetTypes())\r\n                     .Where(t => typeof(IEnumerable).IsAssignableFrom(t))\r\n<\/pre>\n
We actually want to be pickier than that – because we need to work out how to actually instantiate one of these types. So let’s make sure all of our candidate types have a constructor which accepts a single IEnumerable of the passed-in collection type:<\/p>\n
\r\n \u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0        \u00a0\u00a0 .Select(t => { try { return t.MakeGenericType(typeof(T)); } catch { return null; }})\r\n                     .Where(t => t != null && t.GetConstructor(constructorParamTypeArray) != null)\r\n<\/pre>\n
The try\/catch block there is to deal with classes like ConcurrentDictionary, which require multiple generic parameters even though they implement IEnumerable. Is there a better way to check? Probably! But we’re not writing production-grade code here, because .ToRandomCollectionType<>() is fundamentally production-unsuitable anyway.<\/p>\n
The next step is to randomly select one of our candidate types and grab a reference to the right constructor.<\/p>\n
\r\nvar type = types[_rnd.Next(0, types.Count-1)];\r\nvar constructor = type.GetConstructor(constructorParamTypeArray);\r\n<\/pre>\n
Now all that’s left is to invoke the constructor and return the result!<\/p>\n
\r\nreturn (IEnumerable<T>)constructor.Invoke(new [] {collection});\r\n<\/pre>\n
Does it work? Absolutely! Most of the time, anyway. Here’s the outcome of feeding { 1, 2, 3 } into it a few times:<\/p>\n
\"ToRandomCollectionType\"<\/a><\/p>\n
Much like the FileChangeMonitor hack I blogged about<\/a>, this is unsuitable for anything production-like. Please treat it as the humourous hack it is and don’t use it for anything important!<\/p>\n
Hang on though, we’re not done. You should always test your code. Like, with automated tests.<\/p>\n
\r\npublic class ItShouldUsuallyWork\r\n{\r\n    [Test]\r\n    public void TryingAFewTimes_SometimesWorks() {\r\n        var inputSet = new List<int> {1, 2, 3};\r\n        int successCount = 0;\r\n        for (int i = 0; i < 10; i++) {\r\n            var result = inputSet.ToRandomCollectionType();\r\n            try {\r\n                inputSet.Should().BeEquivalentTo(result);\r\n                Console.WriteLine($"Got a {result.GetType()}");\r\n                successCount++;\r\n            }\r\n            catch {\r\n                Console.WriteLine("Looks like that one failed.");\r\n            }\r\n        }\r\n        successCount.Should().BeGreaterOrEqualTo(5);\r\n    }\r\n}\r\n<\/pre>\n
The code is available on GitHub<\/a>, and there is a NuGet package<\/a> so this lovely little extension method is never more than a quick “Install-Package ToRandomCollectionType” away.<\/p>\n
If you enjoy a little C# whimsy, you might like to read about my Object.Extend(…) implementation in C#<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"
If you’ve spent time in the C# world, you’ve probably encountered (and possibly asked) the question: “Should I use .ToList() or .ToArray()?” The answer, of course, is that it’s a false dichotomy: I’ve written before about how you should pick the right data structure for the job. But what if you really don’t care? What … Continue reading New LINQ Method: ToRandomCollectionType<>()<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[18,13,17,12],"tags":[],"yoast_head":"\nNew LINQ Method: ToRandomCollectionType() - Nerdhold Coder<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"http:\/\/www.nerdhold.com\/coder\/2019\/06\/07\/new-linq-method-torandomcollectiontype\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"New LINQ Method: ToRandomCollectionType() - Nerdhold Coder\" \/>\n<meta property=\"og:description\" content=\"If you’ve spent time in the C# world, you’ve probably encountered (and possibly asked) the question: “Should I use .ToList() or .ToArray()?” The answer, of course, is that it’s a false dichotomy: I’ve written before about how you should pick the right data structure for the job. 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