<p>In <a href="https://github.com/mlpack/mlpack/pull/686#discussion_r69383375">src/mlpack/methods/ne/genome.hpp</a>:</p>
<pre style='color:#555'>&gt; +    return aLinkGenes.size();
&gt; +  }
&gt; +
&gt; +  // Whether specified neuron id exist in this genome.
&gt; +  bool HasNeuronId(ssize_t id) const {
&gt; +    for (ssize_t i=0; i&lt;NumNeuron(); ++i) {
&gt; +      if (aNeuronGenes[i].Id() == id) {
&gt; +        return true;
&gt; +      }
&gt; +    }
&gt; +    
&gt; +    return false;
&gt; +  }
&gt; +
&gt; +  // Get neuron by id.
&gt; +  NeuronGene GetNeuronById(ssize_t id) {
</pre>
<p>We could avoid probably expensive copy (NeuronGene), by using a reference:</p>

<p><code>void GetNeuronById(ssize_t id, NeuronGene&amp; gene)</code></p>

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