Re: Derived private interface

[Jeffrey Carter <spam.jrcarter.not@spam.not.acm.org>]

On 07/27/2011 04:56 PM, Randy Brukardt wrote:
>
> I don't agree; the 30 page case statements found in our optimizer and some
> other parts of our compiler don't add anything to ease of reading! And there
> is no choice with case statements, you have to have a bunch of lines for
> each option; when there are literally hundreds of options there is no way to
> simplify.
>
> And updating those cases typically takes about a week's work; it is so time
> consuming that we avoid making changes to the intermediate code if any
> workaround can be found even when that is the best solution to a problem.

There are as many options and as many lines of code per option no matter which 
implementation technique you use. At least with composition they're all together 
in one place; programming by extension puts them in as many places as there are 
options, with no links in the code to tell you where they are; the odds of 
leaving some options unmodified is much greater.

As you mentioned later, it doesn't save you any effort, either.

> I admit that dispatching takes a leap of faith ("it just works" when used
> properly), and not everyone seems to be able to understand it. But having a
> lot less code in the critical parts of the application should help
> understanding.

Everyone I know who has worked with code that uses programming by extension 
misunderstands it at least some of the time. (Perhaps you are an exception.) 
Composition does not seem to have this problem.

-- 
Jeff Carter
"Propose to an Englishman any principle, or any instrument, however
admirable, and you will observe that the whole effort of the English
mind is directed to find a difficulty, a defect, or an impossibility
in it. If you speak to him of a machine for peeling a potato, he will
pronounce it impossible: if you peel a potato with it before his eyes,
he will declare it useless, because it will not slice a pineapple."
Charles Babbage
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