title: error: passing ‘const std::__cxx11::list<>’ as ‘this’ argument discards qualifiers
body: <p>I have a little problem and can't find a way to fix it..</p>
  
  <p>In my .hpp file I have declared these two functions and struct but getting the error  'passing ‘const std::__cxx11::list&lt;>’ as ‘this’ argument discards qualifiers.'</p>
  
  <pre><code>struct Student {
      std::string name;
      std::string student_id;
  
  };
  
  class StudentRegistry {
  
  public:
      StudentRegistry(){}
      void Add(const Student &amp;t);
      const std::list&lt;Student&gt;&amp; GetStudents() const;
  
  private:
      std::list&lt;Student&gt; students;
  };
  </code></pre>
  
  <p>And in .cpp file I have tried to do:</p>
  
  <pre><code>void StudentRegistry::Add(const Student &amp;t){
      this-&gt;GetStudents().push_back(t);
  }
  
  const std::list&lt;Student&gt;&amp; StudentRegistry::GetStudents() const{
      return students;
  }
  </code></pre>
  
  <p>How can I make this work?</p>