title: c++: Swap first and second element for all tuples in a vector
body: <p>is there a way to swap the first and second elements for all tuples in a vector?
  Let's say I have something like this:</p>
  
  <pre><code>#include&lt;vector&gt;
  #include&lt;tuple&gt;
  
  int main()
  {
  std::vector&lt;std::tuple&lt;int,int&gt;&gt; my_vector;
  my_vector.push_back(std::make_tuple(1,2));
  my_vector.push_back(std::make_tuple(3,4));
  }
  </code></pre>
  
  <p>The first elements of the tuple are now 1 and 3 with the second elements being 2 and 4. Is there an easy to make 2 and 4 the first elements?</p>