rder-radius: 3px; border: 1px solid #cccccc;">std::vector&lt;bool&gt;</code>, whose substript operator (<code style="color: #000000; font-family: monospace,monospace; padding: 0.1em 0.2em; margin: 0.1em; font-size: 85%; background-color: #F5F5F5; border-radius: 3px; border: 1px solid #cccccc;">operator[]</code>) does not actually return a reference to a real bool and definitely not to a bit, but actually returns a proxy object of type <code style="color: #000000; font-family: monospace,monospace; padding: 0