Re: MV Keys (was: Key attributes with list values)

David Cressey wrote:
>
> The way Pick (and I presume most of the MV family) represent lists is
> inherently ordered. And, whenever I ask Dawn, or any of the other Pickies
> who dorp in form time to time whether the order in a list conveys
> information or not, the answer is always the same:
> "the programmer knows what the data means".

This error is endemic to computer programming. For example, most Java programmers in most contexts will use a java.util.List as storage for unordered collections. It is even in the stardard library that way.

Lists are just fantastically easy to implement and fantastically easy to use, and so they get used for things whether it makes sense or not. And when I point this out to most people, they ask "where's the harm?"

The harm is the same as always comes from overspecifying. The system can only work with what it knows, and if you told it a collection was a list, it's going to studiously keep the elements in order, even though it doesn't need to. Opportunities for optimization are lost. Further, it can leak into the semantic level. Is this equation correct? [a, b] != [b, a]. If you are using an ordered collection to represent unordered data, you'll get the wrong answer.

A line I remember from years ago: "It's not that polar coordinates are difficult. It's just that rectangular coordinates are easier than they have any right to be."

Substitute set and list and it still works. :-)

Marshall Received on Mon Feb 27 2006 - 01:54:24 CET