Re: Inheritance Issue
Al wrote:
I have been dealing with an issue that has cropped up several times
and I'm not sure what the best approach is. In its simplest form,
the problem is:
class Base { ... };
class Derived : public Base { public: int Field; };
Now, somewhere else I have:
void foo(Base* base) {
// if (base is Derived)
// do something with Field.
<snip>
I realize that this doesn't really fix the problem, but the syntax
is a little nicer :). Anyway, between these two, which seems
better? Are there other approaches?
[..]
Victor Bazarov wrote:
If 'foo' doesn't care about 'Field' but should instruct 'Base' to do
something special (that might affect 'Field'), it should be a virtual
function in 'Base' that does nothing itself, but allows 'Derived' to
do what is needed.
Al wrote:
Ok, let me ask a different question: Does it make sense to have a
Do-Nothing base virtual function where in 99% of the derived cases it
does nothing but it does something for just one class? Would that be a
better design?
Either that or a dynamic_cast<Derived*>(base). It's ugly, it's very
bad code to maintain, but it will get you where you seem to want to be.
if (Derived *pd = dynamic_cast<Derived*>(base))
do_something_with(pd->Field);
Of course, you need to write two screenfuls of comments to explain why
you are using such construct, and that's where you blame your lex/yacc
combination, your boss, lack of time, etc.
V
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