<p>In <a href="https://github.com/mlpack/mlpack/pull/686#discussion_r69383600">src/mlpack/methods/ne/neat.hpp</a>:</p>
<pre style='color:#555'>&gt; +    return -1;
&gt; +  }
&gt; +
&gt; +  // Add a new link innovation.
&gt; +  LinkInnovation AddLinkInnovation(ssize_t fromNeuronId, ssize_t toNeuronId) {
&gt; +    LinkInnovation linkInnov;
&gt; +    linkInnov.fromNeuronId = fromNeuronId;
&gt; +    linkInnov.toNeuronId = toNeuronId;
&gt; +    linkInnov.newLinkInnovId = aNextLinkInnovId++;
&gt; +    aLinkInnovations.push_back(linkInnov);
&gt; +
&gt; +    return linkInnov;
&gt; +  }
&gt; +
&gt; +  // Add a new neuron innovation.
&gt; +  NeuronInnovation AddNeuronInnovation(ssize_t splitLinkInnovId) {
</pre>
<p>This also looks like if we would use a reference we could avoid an extra copy:</p>

<p><code><br>
AddNeuronInnovation(ssize_t splitLinkInnovId, NeuronInnovation&amp; neuronInnov)<br>
</code></p>

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