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copied!<p>First, I'll explain why you wouldn't want to use <code>for</code>, and then explain why you might.</p> <p>The main reason you wouldn't want to use <code>for</code> is that it's un-idiomatic. If you use <code>each</code>, you can easily replace that <code>each</code> with a <code>map</code> or a <code>find</code> or an <code>each_with_index</code> without a major change of your code. But there's no <code>for_map</code> or <code>for_find</code> or <code>for_with_index</code>.</p> <p>Another reason is that if you create a variable within a block within <code>each</code>, and it hasn't been created before-hand, it'll only stay in existance for as long as that loop exists. Getting rid of variables once you have no use for them is a good thing.</p> <p>Now I'll mention why you might want to use <code>for</code>. <code>each</code> creates a closure for each loop, and if you repeat that loop too many times, that loop can cause performance problems. In <a href="https://stackoverflow.com/a/10325493/38765">https://stackoverflow.com/a/10325493/38765</a> , I posted that using a <code>while</code> loop rather than a block made it slower. </p> <pre><code>RUN_COUNT = 10_000_000 FIRST_STRING = "Woooooha" SECOND_STRING = "Woooooha" def times_double_equal_sign RUN_COUNT.times do |i| FIRST_STRING == SECOND_STRING end end def loop_double_equal_sign i = 0 while i < RUN_COUNT FIRST_STRING == SECOND_STRING i += 1 end end </code></pre> <p><code>times_double_equal_sign</code> consistently took 2.4 seconds, while <code>loop_double_equal_sign</code> was consistently 0.2 to 0.3 seconds faster.</p> <p>In <a href="https://stackoverflow.com/a/6475413/38765">https://stackoverflow.com/a/6475413/38765</a> , I found that executing an empty loop took 1.9 seconds, whereas executing an empty block took 5.7 seconds.</p> <p>Know why you wouldn't want to use <code>for</code>, know why you would want to use <code>for</code>, and only use the latter when you need to. Unless you feel nostalgic for other languages. :)</p>

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