`How to fix undefined method `[]' for nil:NilClass
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<div class="content__item-top-div"> <a class="content__item-top-name" href="#!">Roman Tomchenko</a><span class="content__item-top-p">2020-10-15 08:19:34</span></div>
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<div class="content__item-row dn"> <a href="#!"><b>Roman Tomchenko</b>,</a> 2020-10-15 08:19:34</div>
<p class="content__item-title large">How to fix undefined method `[]' for nil:NilClass?</p>
<p class="content__item-detail sm">
There is an array<br>
<pre><code class="ruby hljs">LINE = [
<span class="hljs-string">' '</span>, <span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>, <span class="hljs-string">'d'</span>, <span class="hljs-string">'e'</span>, <span class="hljs-string">'f'</span>, <span class="hljs-string">'g'</span>, <span class="hljs-string">'h'</span>, <span class="hljs-string">'i'</span>, <span class="hljs-string">'j'</span>, <span class="hljs-string">'k'</span>, <span class="hljs-string">'l'</span>, <span class="hljs-string">'m'</span>, <span class="hljs-string">'n'</span>, <span class="hljs-string">'o'</span>, <span class="hljs-string">'p'</span>, <span class="hljs-string">'q'</span>, <span class="hljs-string">'r'</span>, <span class="hljs-string">'s'</span>, <span class="hljs-string">'t'</span>,
<span class="hljs-string">'u'</span>, <span class="hljs-string">'v'</span>, <span class="hljs-string">'w'</span>, <span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>, <span class="hljs-string">'z'</span>, <span class="hljs-string">'A'</span>, <span class="hljs-string">'B'</span>, <span class="hljs-string">'C'</span>, <span class="hljs-string">'D'</span>, <span class="hljs-string">'E'</span>, <span class="hljs-string">'F'</span>, <span class="hljs-string">'G'</span>, <span class="hljs-string">'H'</span>, <span class="hljs-string">'I'</span>, <span class="hljs-string">'J'</span>, <span class="hljs-string">'K'</span>, <span class="hljs-string">'L'</span>, <span class="hljs-string">'M'</span>, <span class="hljs-string">'N'</span>, <span class="hljs-string">'O'</span>,
<span class="hljs-string">'P'</span>, <span class="hljs-string">'Q'</span>, <span class="hljs-string">'R'</span>, <span class="hljs-string">'S'</span>, <span class="hljs-string">'T'</span>, <span class="hljs-string">'U'</span>, <span class="hljs-string">'V'</span>, <span class="hljs-string">'W'</span>, <span class="hljs-string">'X'</span>, <span class="hljs-string">'Y'</span>, <span class="hljs-string">'Z'</span>, <span class="hljs-string">'!'</span>, <span class="hljs-string">','</span>, <span class="hljs-string">'.'</span>, <span class="hljs-string">':'</span>, <span class="hljs-string">';'</span>, <span class="hljs-string">'-'</span>
]</code></pre><br>
<br>
There is a hash that is formed like this:<br>
<pre><code class="ruby hljs">$square = Hash.new
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">build_square</span></span>
LINE.each { <span class="hljs-params">|c|</span> $square[c] = LINE.rotate(LINE.index(c)) }
<span class="hljs-keyword">end</span>
build_square</code></pre><br>
<br>
That is, the hash key is a character, the value is an array. <br>
When it comes out, everything is fine. <br>
However, when getting a hash value into a variable, the result is not indexed (text, key are regular strings of equal length).<br>
<pre><code class="ruby hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">encode</span><span class="hljs-params">(text, key)</span></span>
res = <span class="hljs-string">""</span>
(<span class="hljs-number">0</span>..text.size).each <span class="hljs-keyword">do</span> <span class="hljs-params">|i|</span>
line = $square[key[i]]
n = LINE.index(text[i])
res += line[n]
<span class="hljs-keyword">end</span>
res
<span class="hljs-keyword">end</span></code></pre><br>
<br>
In the line <b>res += line[n]</b> gives an error <i>undefined method `[]' for nil:NilClass</i><br>
<br>
Just started to understand Ruby - I can not understand something, but when outputting line - everything is fine, it is output as an array.
</p>
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<div class="content__item-img large name-color-V"><span>V</span></div><span class="answer__name"><a href="#!">Valentin V.</a>, 2020-10-15 <br/> @Widestrip</span>
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<p class="answer__detail"><code class="hljs">line = $square[key[i]]</code><br>
There are characters in the key string that are not in either $square or the LINE constant, as a result, at one of the iterations, the line variable is equal to nil</p>
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