[Oberon] How to mimic an associative array

[Jörg Straube]

> Hi
> 
> I followed the discussion for a while, and up to now saw
> TWO different solutions to your original question:
> 
> 1) proposed by Sven
>   TYPE
>     AssociativeArray = OBJECT
> 	PROCEDURE get(key : String) : String;
> 	PROCEDURE put(key, value : String);
> 	PROCEDURE remove(key : String);
>     END AssociativeArray;
> 
> 2) proposed by Aubrey
>   TYPE
>      myHashPtr = POINTER TO myHash;
> 
>   PROCEDURE Init* (VAR t : myHash); 
>   PROCEDURE Enter* (VAR t: myHash, key: keyType, value: valueType); 
>   PROCEDURE This* (t : myHash, key: keyType, VAR valueType);
>   PROCEDURE Remove* (VAR t: myHash, key : keyType);
>   PROCEDURE Enumerate* (t : myHash, handler : someProcType);
> 
> Aubrey took more the "classical" procedural approach à la Pascal or Modula.
> Sven proposed the object approach possible in Oberon.
> 
> Personally, I like Sven's approach more. (In Sven's mail you even find
> a complete Oberon implementation for his OBJECT). But you can see that
> there are different approaches to model and implement a given problem
> or data structure.
> 
> In other languages you write
>   capital['england'] = 'london'
>   location = capital['england']
> 
> With Sven's approach you would write
>   VAR capital: AssociativeArray;
>   capital.put('england', 'london');
>   location := capital.get('england');
> 
> 
> Associative Arrays are called differently in different programming languages
> - "dictionary" in e.g. Python and Objective-C
> - "hash" in e.g. Perl and Ruby
> - "map" in e.g. C++ and Java
> 
> I guess the wording "hash" used by Perl generated some confusion, as in computer
> science a "hash" normally describes a mapping function to a countable set of values.
> Others already pointed out that an associative array can be implemented using a
> hash function. BTW Sven used (a very simple) hash function in his proposed
> implementation. Have a look at his mail, it gives quite some good insight in how to
> program in Oberon.
> 
> Merry xmas!
> Joerg

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