Initialization of a reference versus initialization of an object

Question

I know dynamic casts works on pointers and references. Both of the following work casting downwards

der d;
base& b = d;
der x = dynamic_cast<der&>(b);  -->A
der& y = dynamic_cast<der&>(b); -->B
x.method();
y.method();

I wanted to know what the difference is between A and B

You don't need any cast at all to convert from derived to base. — aschepler, Nov 23 '14 at 22:29
The difference between A and B doesn't involve `dynamic_cast` at all. Are you asking what the difference is between a value type and a reference? — Drew Dormann, Nov 23 '14 at 22:33
Still wrong. If `b` is an actual object, not a reference, the cast will always throw. Also, you've mixed up `der` vs `base` and `B` vs `A`, making it very confusing. — Sebastian Redl, Nov 23 '14 at 22:36
Your example has nothing to do with `dynamic_cast`. Changed the title accordingly. — Cheers and hth. - Alf, Nov 23 '14 at 22:40

score 2 · Accepted Answer · answered Nov 23 '14 at 23:36

The line

der x = dynamic_cast<der&>(b);

constructs an object of type der and initializes it with dynamic_cast<der&>(b)

The line

der& y = dynamic_cast<der&>(b);

just initializes a reference.

x.method();

calls method() on the separately constructed object.

y.method();

calls method() on the object y references, which is d.

1 Answers1