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copied!<p>Let's build this up step-by-step. We will simplify things a bit by taking it out of the class context.</p> <p>For this example it is intuitive to think of an iterator as being a more-powerful replacement for a traditional for-loop. </p> <p>So first here's a for-loop version:</p> <pre><code>seq1 = (0..2) seq2 = (0..2) for x in seq1 for y in seq2 p [x,y] # shorthand for puts [x, y].inspect end end </code></pre> <p>Now let's replace that with more Ruby-idiomatic iterator style, explicitly supplying blocks to be executed (i.e., the <code>do...end</code> blocks):</p> <pre><code>seq1.each do |x| seq2.each do |y| p [x,y] end end </code></pre> <p>So far, so good, you've printed out your cartesian product. Now your assignment asks you to use <code>yield</code> as well. The point of <code>yield</code> is to "yield execution", i.e., pass control to another block of code temporarily (optionally passing one or more arguments).</p> <p>So, although it's not <em>really</em> necessary for this toy example, instead of directly printing the value like above, you can <code>yield</code> the value, and let the caller supply a block that accepts that value and prints it instead.</p> <p>That could look like this:</p> <pre><code> def prod(seq1, seq2) seq1.each do |x| seq2.each do |y| yield [x,y] end end end </code></pre> <p>Callable like this:</p> <pre><code>prod (1..2), (1..2) do |prod| p prod end </code></pre> <p>The <code>yield</code> supplies the product for each run of the inner loop, and the yielded value is printed by the block supplied by the caller.</p>

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