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.NET/C# Lambda Expressions

By Dag, on December 30th, 2016

using System.Linq;

The >= lambda operator in .NET can be a really handy match expression tool. By using lambda expressions, you can write local functions that can be passed as arguments or returned as the value of function calls. To create a lambda expression, you specify input parameters (if any) on the left side of the lambda operator =>, and you put the expression or statement block on the other side. For example, the lambda expression x => x * x specifies a parameter that’s named x and returns the value of x squared. Here I add a few times I've used it for reference.

Finding the last item in a list:

List<string s> l = new List<string s>();
string TheLastItem = l.FindLast((string ListItem) => ListItem.Length > 5);

Equivalent to:

List<string s> l = new List<string s>();
String TheLastItem;
foreach (string ListItem in l) {
	if (ListItem.Length > 5)
		TheLastItem = ListItem; // Will end up with the last.
}

Array ordering:

PopLines = PopLines.OrderByDescending(line => Int32.Parse(line.Split('\t')[1])).ToArray();

EventHandler:

p.Exited += (object senderr, EventArgs ee) => { Program_IsRunning["mailpv"] = false; };

Sorting files by creation date:

DirectoryInfo MBAMLogDirInfo = new DirectoryInfo(MBAMLogDir);
FileInfo[] MBAMLogs = MBAMLogDirInfo.GetFiles("mbam-log-*").OrderByDescending(f => f.CreationTime).ToArray();

Check if a service exists:

ServiceController ctl = ServiceController.GetServices().FirstOrDefault(s => s.ServiceName == "VPNBypassService");
if (ctl != null)
	return true;
else
	return false;

Coming from other languages, the lambda expression/operator tend to give a powerful first impression.