title: Disable copy constructor
body: <p>I have a class:</p>
  <pre><code>class SymbolIndexer {
  protected:
    SymbolIndexer ( ) { }
  
  public:
    static inline SymbolIndexer &amp; GetUniqueInstance ( ) 
    { 
      static SymbolIndexer uniqueinstance_ ;
      return uniqueinstance_ ; 
    }
  };
  </code></pre>
  <p>How should I modify it to disable code like:</p>
  <pre><code>SymbolIndexer symbol_indexer_ = SymbolIndexer::GetUniqueInstance ( );
  </code></pre>
  <p>and only allow code like:</p>
  <pre><code>SymbolIndexer &amp; ref_symbol_indexer_ = SymbolIndexer::GetUniqueInstance ( );
  </code></pre>