template <typename T>
optional<T&> foo()
{
...

    optional<T> o;

    if(x)
    {
        o = p1();
        //Use o
    
        o = p2();
        //Use o
    
        o = q1();
        //Do 1
    }
    
    if(y)
    {
        o = q2();
        //Do 2
    }
    
    if(o)
    {
        //Do 3
    }
    
    switch ( cond )
    {
    case a : o = foo1(); break ;
    case b : o = foo2(); break ;
    case c : o = foo3(); break ;
    case d : o = foo4(); break ;
    case e : o = foo5(); break ;
    
    default :  // o remains uninitialized
    }
    
    if(o)
    {
        //Do 4.
    }
    
    o = foo8();
    
    //Do 5.
}