[Newbies] Best way to implement two-dimensional array

John Almberg jalmberg at identry.com
Tue Sep 4 12:58:19 UTC 2007

Hi Goran,

> Mmmm, I feel I must ask the "why?" question here. :) What are you  
> actually
> trying to implement? The reason I ask is because it looks like you  
> may be
> falling into the trap of "data objects" (creating structures of  
> data with
> no real behaviors).

Yes, that's an accurate description of what I'm trying to model: the  
Movement Table from a very complicated, 'age of sail' board game. The  
table models the speed of 9 classes of sailing ships at various wind  
speeds, sail settings, damage, and points of sail.

Thus it describes or summarizes some of the sailing attributes of  
these 9 classes of ships. I've studied the table to see if it could  
be computed, rather than simply stored, but I think the table  
summarizes empirical data gleaned from historical records, rather  
than a mathematical function, so not easy to model without a table.

I have use polymorphism to break the one massive table into 9 smaller  
tables, one in each of the 9 classes of ships (children of class Ship).

I'm storing them in a class variable and using it, more or less, as a  
constant lookup table. There isn't much behavior in the table itself,  
but it models behavior, if you see what I mean.

And there is plenty of other behavior in the ship classes, as you can  

The real 'why' is fun. I've been wanting to learn Smalltalk and to  
program a game like this for about 25 years. With Squeak on a Mac,  
and a pile of Smalltalk books bought second-hand from Amazon, I'm  
making some progress. With the side benefit of learning some new  
tricks that help my Ruby programming (my day job).

>> Or, I'm thinking it might be simpler to leave the literal as an
>> array, and do the castings as necessary during access, like this:
> The word "casting" is not generally used in the Smalltalk context  
> given
> that Smalltalk is not statically typed. #as: is a message send and it
> creates a new object of the given class. You can see what it does by
> looking at Object>>as:.

Sorry... still learning the Smalltalk jargon.

> You can do it in several ways - it's just "code". If you only need  
> Symbols
> and literals as above you could use regular Array syntax (it only
> evaluates literals - not expressions - and it is constructed at  
> compile
> time):
> | result dict |
> result := Dictionary new.
> #(
> 	(fs (C 0  B 1  R 0))
> 	(gs (C 7  B 5  R 4))
> 	(gs (C 7  B 5  R 4))
> ) do: [:arr |
> 	dict := Dictionary new.
> 	arr second pairsDo: [:a :b | dict at: a put: b].
> 	result at: arr first put: dict].
> result

This is an interesting approach, too. I'm currently thinking that I  
don't really need to store the data as a dictionary... my main  
concern is to format the table(s) in a way that is easy for *me* to  
read (so I can find and fix the inevitable typos.)

I don't really care if the computer has to do some heavy lifting to  
*access* the data. It's not something that has to be fast. So I'm  
going to go for an approach that maximizes the human readability of  
the data, and pushes the complicated bits into the accessors.


-- John

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