Warp wrote:
>   Switch-case blocks are not that much faster compared to dynamic binding.

They are not by code, but by design. As I outlined, you get an impenetrable
mess of dependent methods. That is slow. How slow? Well, it depends on the
object's details. Expect up to twice the time required for processing. Does
that translate to 20% or 50% or more slowdown? Implementing would tell, but
no need to implement something already known to be slower. As I said, I have
done it before. How fast was it to begin with - the VRML 97 I worked on was
faster than the equivalent generated by a standard C parser generator. For
some unfortunate VRML 97 object types abstraction on a method level would
cause needlessly complicated detached processing that ate most of the
parser's performance compared to the parser generator version.

>   A well-implemented parser *abstracts* away these implementation details.

That is pure theory and completely inappropriate for maintainable code.

>   I see no reason why adding a new token could not be done by simply
> adding the name of a new class in one .cpp file (besides implementing
> that new class, of course).

Well, from experience I know there are good reasons to make certain choices
for speed and maintainability. So I guess in the end it just comes down to
believing in my experience in building very fast and maintainable parsers,
including all the lessons learnt from problems caused by overdoing the
design abstraction. The best theory simply isn't always the best (in all
dimensions) implementation.

	Thorsten

Post a reply to this message