title: How to merge two hashes without losing values
body: <p>I have two hashes like these.</p>
  
  <pre><code>a = {foo: {first: 1}, bar: {first: 2}}
  b = {foo: {second: 3}, bar: {second: 4}}
  </code></pre>
  
  <p>And I expected as a result of <code>a.merge b</code> like this.</p>
  
  <pre><code>{foo: {first: 1, second: 3}, bar: {first: 2, second: 4}}
  </code></pre>
  
  <p>But <code>a.merge b</code> returns <code>{:foo=&gt;{:second=&gt;3}, :bar=&gt;{:second=&gt;4}}</code>.</p>
  
  <p>How can I merge two hashes without losing values?</p>