title: How to convert a json object to a map with nlohmann::json?
body: <p>For example, with nlohmann::json, I can do </p>
  
  <pre><code>map&lt;string, vector&lt;int&gt;&gt; m = { {"a", {1, 2}}, {"b", {2, 3}} };
  json j = m;
  </code></pre>
  
  <p>But I cannot do</p>
  
  <pre><code>m = j;
  </code></pre>
  
  <p>Any way to convert a json object to a map with nlohmann::json?</p>