Tutorial :What part of the C# language is .ForEach()?


If I'm explaining the following ForEach feature to someone, is it accurate to say that #2 is the "LINQ foreach approach" or is it simply a "List<T> extension method" that is not officially associated with LINQ?

var youngCustomers = from c in customers                       where c.Age < 30                       select c;    //1. traditional foreach approach  foreach (var c in youngCustomers)  {      Console.WriteLine(c.Display());  }    //2. LINQ foreach approach?  youngCustomers.ToList().ForEach(c => Console.WriteLine(c.Display()));  


it is a normal method of List<T> though people often provide their own extension methods for other IEnumerable<T>. LINQ does not provide a ForEach extension due to its design goals of being functional/ working with immutable types, ForEach is an inherently side effect/imperative operation.


It has nothing to do with LINQ and it's not an extension method.

ForEach is a plain instance method on the List<T> class.

(And if you wanted to be really nitpicky, then ForEach is not part of the C# language at all: it's part of the .NET Base Class Library.)


It is not an extension method of List<T>, it is a regular method of List<T>.

So it has nothing to do with LINQ. If it had, the distinction between "officially associated with LINQ" and not officially associated with LINQ is not practically a very useful one. LINQ is simply a bunch of chained extension methods (often on IEnumerable<T>). There is rarely any point in distinguishing it from other extension methods on IEnumerable<T>. The best distinction would be that they reside in one of the System.Linq or System.Something.Linq namespaces.


It's not LINQ. One of the design aspects of LINQ is that the standard LINQ methods do not have side-effects. The ForEach method would violate this.

Eric Lippert has a blog article all about this:



youngCustomers.ToList().ForEach(c => Console.WriteLine(c.Display()));   

Let's break it down:

  • ToList is a call to System.Linq.Enumerable.ToList() introduced in .net framework 3.5
  • ForEach is a call to System.Collections.Generic.List<T>.ForEach introduced in .net framework 2.0
  • c => is lambda expression syntax introduced in c# 3.0.

If you look at the documentation for List<T>.ForEach, you can see the old delegate syntax that was required back then to call it.


Side-effecting foreach will be ( is ) provided in Visual Studio 2010's Linq extensions.

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