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POList<T>.ForEach vs. custom IEnumerable<T> extension
 

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  1. POList<T>.ForEach vs. custom IEnumerable<T> extension
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    <p>Say I have a class:</p> <pre><code>public class MyClass { ... } </code></pre> <p>and a webservice method that returns an <code>IEnumerable&lt;MyClass&gt;</code></p> <p>The consumer of the webservice defines some method:</p> <pre><code>public void DoSomething(MyClass myClass) { ... } </code></pre> <p>Now, the consumer can call <code>DoSomething</code> on the result of the webservice method in two ways:</p> <pre><code>var result = // web service call foreach(var myClass in result) { DoSomething(myClass); } </code></pre> <p>or:</p> <pre><code>var result = // web service call result.ToList().ForEach(DoSomething); </code></pre> <p>Needless to say I much prefer the second way since it is much shorter and more expressive (once you get used to the syntax, which I have).</p> <p>Now, the web service method only exposes an <code>IEnumerable&lt;MyClass&gt;</code>, but it actually returns a <code>List&lt;MyClass&gt;</code> which (AFAIK) means that the actual serialized object is still a <code>List&lt;T&gt;</code>. However, I have found (using reflector) that the Linq method <code>ToList()</code> makes a copy of all the objects in the <code>IEnumerable&lt;T&gt;</code> regardless of the actual runtime type (in my opinion, it could just have casted the argument to a <code>List&lt;T&gt;</code> if it already was one). </p> <p>This obviously has some performance overhead, especially for large list (or lists of large objects).</p> <p>So what can I do to overcome this problem, and why is there no <code>ForEach</code> method in Linq?</p> <p>By the way, his question is vaguely related to <a href="https://stackoverflow.com/questions/2297100/wcf-operationcontract-which-generic-collection-type-should-i-expose">this one</a>.</p>
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    1. USKlaus Byskov Pedersen
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    1. CO"why is there no ForEach method in Linq?": http://stackoverflow.com/questions/800151/why-is-foreach-on-ilistt-and-not-on-ienumerablet
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    2. CO`ToList()` does not make a copy of the objects unless they are value type. Instead, it creates a list with the same references, which allows a modification of the original list when the loop is still active (in some situation you may want this). It also allows the use of a variable delegate, in case the `DoSomething` action depends on something else or is an argument, and that is probably the case where `ForEach` makes sense - although you could do without.
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