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POSpecial closure use-cases: Why use closures?
 

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    <h2>Update</h2> <p>I am designing an experimental programming language and the question is wether to include closures or just use first-class-functions. To decide this i need realistic use-cases/examples that show the benefit of closures over first-class-functions. I know that you can achieve <em>everything</em> that you can achieve with one of the two <em>without them</em>, but there are several use-cases for e.g. first-class-functions where the code is easier to read (e.g. shorter or not split up into several classes). E.g:</p> <p>Ruby:</p> <pre><code>[1,5,7].map{|x| x*x } [1,'test',3].select{|x| x.kind_of? Integer}.map{|x| x.to_s } big_array.each{ |item| puts item } </code></pre> <p>Without first-class-functions these examples would be a lot more verbose, since you would have to use for-loops or similar things.</p> <p>Now, what use-cases show the usefulness of closures? Even though i use first-class-functions a lot, i really could not come up with good use-cases for closures. Do you have any good use-cases for closures?</p> <h2>Original Post</h2> <p>I dont get why closures bind to <em>variables</em> and not just to <em>values</em>, e.g.:</p> <p>Ruby:</p> <pre><code>x = 5 l = lambda { x } l.call #=&gt; 5 x = 100 l.call #=&gt; 100 </code></pre> <p>Whats the use in referencing variables instead of just referencing the values stored in the variables at the point of definition of the closure? Like in this example:</p> <p>Ruby:</p> <pre><code>x = 5 l = lambda { x } l.call #=&gt; 5 x = 100 l.call #=&gt; 5, not 100 </code></pre> <p>Are there good use-cases where it is necessary to reference <em>variables</em> instead of just the <em>values</em> of those variables at the point of definition of the closure?</p>
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