Re: Identifiying which derived class you have in code
On Sep 12, 4:35 pm, "Alf P. Steinbach" <al...@start.no> wrote:
* James Kanze:
On Sep 12, 5:46 am, "Alf P. Steinbach" <al...@start.no> wrote:
* Christopher:
As always, remember to measure.
It might be that this attempt at optimization will have
little, no or even negative effect (such is difficult to
predict, measurement is needed).
It's rather obvious that maintaining code with 10 or more
dynamic_cast's is very expensive. I don't think you need to
measure that.
The alternative to optimization isn't another and extremely
silly attempt at optimization, it's simply to not optimize
(manually), i.e. using a common interface for everything
regardless of whether there is a special case.
Whether using another, derived interface optimized development
times or not depends on the case at hand. If the added
functionality is non-trivial, I find it much clearer to have a
separate interface to access it. Having done that, it really
doesn't matter whether you provide a special function in the
base class to return a (possibly null) pointer to this
interface, or use dynamic_cast. But dynamic_cast is already
implemented, so is probably more cost-effective.
And then, relative to no optimization a check for special case
will cause branching, and it will most probably cause slightly
(microscopically) larger code size, which can influence
caching, and with your proposed way of checking (dynamic cast)
instead of my proposed way of checking, the check itself will
likely be "expensive" relative to the code it guides.
Thus, the only way to be sure about the effect is to measure.
But you can't measure except by implementing both, and that's
definitely more expensive than choosing which ever seems most
reasonable, and just using it.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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