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    <p>Closures are simply great tools. When to use them? Any time you like... As has already been said, the alternative is to write a class; for example, pre C# 2.0, creating a parameterised thread was a real struggle. With C# 2.0 you don't even need the `ParameterizedThreadStart' you just do:</p> <pre><code>string name = // blah int value = // blah new Thread((ThreadStart)delegate { DoWork(name, value);}); // or inline if short </code></pre> <p>Compare that to creating a class with a name and value</p> <p>Or likewise with searching for a list (using a lambda this time):</p> <pre><code>Person person = list.Find(x=&gt;x.Age &gt; minAge &amp;&amp; x.Region == region); </code></pre> <p>Again - the alternative would be to write a class with two properties and a method:</p> <pre><code>internal sealed class PersonFinder { public PersonFinder(int minAge, string region) { this.minAge = minAge; this.region = region; } private readonly int minAge; private readonly string region; public bool IsMatch(Person person) { return person.Age &gt; minAge &amp;&amp; person.Region == region; } } ... Person person = list.Find(new PersonFinder(minAge,region).IsMatch); </code></pre> <p>This is <em>fairly</em> comparable to how the compiler does it under the bonnet (actually, it uses public read/write fields, not private readonly).</p> <p>The biggest caveat with C# captures is to watch the scope; for example:</p> <pre><code> for(int i = 0 ; i &lt; 10 ; i++) { ThreadPool.QueueUserWorkItem(delegate { Console.WriteLine(i); }); } </code></pre> <p>This might not print what you expect, since the <em>variable</em> i is used for each. You could see any combination of repeats - even 10 10's. You need to carefully scope captured variables in C#:</p> <pre><code> for(int i = 0 ; i &lt; 10 ; i++) { int j = i; ThreadPool.QueueUserWorkItem(delegate { Console.WriteLine(j); }); } </code></pre> <p>Here each j gets captured separately (i.e. a different compiler-generated class instance).</p> <p>Jon Skeet has a good blog entry covering C# and java closures <a href="http://msmvps.com/blogs/jon_skeet/archive/2008/05/06/the-beauty-of-closures.aspx" rel="noreferrer">here</a>; or for more detail, see his book <a href="http://www.manning.com/skeet/" rel="noreferrer">C# in Depth</a>, which has an entire chapter on them.</p>
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    1. USMarc Gravell
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    1. COSlightly off-topic, but could you suggest how to pronounce "Person person = list.Find(x=>x.Age > minAge && x.Region == region);" if read aloud?
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    2. CO"assign variable person (of type Person) with list.Find: x goes to x.Age greater than minAge and x.Region equals region". Although I'd probably abbreviate to: "...with list.Find where Age greater than minAge and Region equals region.". But "goes to" is a common interpretation of "=>".
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    3. CORegarding this, you might be interested in answering http://stackoverflow.com/questions/1962539/using-closures-to-keep-track-of-a-variable-good-idea-or-dirty-trick :)
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