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POuse of goto versus runtime code evaluation
 

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    <p>Recently for a programming class, we were given the assignment to write a program in any language that, given <em>n</em>, will produce all the possible derangements for an array <em>p</em> of size <em>n</em> such that <em>p</em>[i] != i for all i: 0 &lt;= i &lt; n. We had to use iterators, e.g. <code>yield</code>.</p> <p>Example: n=3, [0, 1, 2] is not a derangement, but [2, 0, 1] is as well as [1, 2, 0].</p> <p>I came up with a pseudocode solution that would work, but the problem was that it required power loops (that is, <em>n</em> nested loops where <em>n</em> is only known at runtime). To do this, I generated <em>n</em> nested loops in Ruby code in a string, then <code>eval</code>-ed the string. My solution worked, however my professor thought that using a few <code>goto</code>s would have been better solution (easier to read, at least) than dynamic code generation.</p> <p>I was under the impression that <code>goto</code> was always a bad choice. Why might runtime evaluation of dynamically generated code be a worse choice than <code>goto</code>? The generated code is clean and simple, and seems fairly efficient for the given problem. The only user input upon which the code generation depends is <em>n</em>, which is checked to ensure it's an integer value beforehand. It <code>yield</code>s only unique derangements, as it should.</p> <p>I'm not asking for a solution to my programming assignment, I just want to know reasons behind the use of <code>goto</code> over dynamic code evaluation, or vice versa.</p> <p><strong>Edit:</strong> to clarify, the assignment included writing a program using iterators and another using recursion, so the iterative version wasn't necessarily meant to be efficient.</p>
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    1. COI think the prof wanted you to do a recursive solution (which is probably the cleanest simplest solution) and then to understand how to simulate a recursive solution using a stack and a goto. The goto solution is simpler and easier to understand than dynamic code generation, because the recursive solution is so simple and understanding a simulated procedure call using a goto is also simple. See the 2 solutions (recursive and simulated recursion using goto) posted below.
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      1. USLarry Watanabe
 

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