[erlang-questions] Hungarian notation for Erlang / ETL

David Holz <>
Wed Jan 9 23:24:06 CET 2008


[I really wish reply-to was set to , or maybe hotmail is just stupid.  Yet again, I accidentally first replied to the sender instead of the list.]

From: 
> 2. I wasn't talking about implementing object using Erlang processes. I
> talking about much simpler and functional solution, like providing
> behaviour, like:
>
> -module(collection).
> -export([behaviour_info/1]).
>
> -module(queue).
> -behaviour(collection).
>
> %% ...
>
> -module(set).
> -behaviour(collection).
>
> %% ...
>
> -module(stack).
> -behaviour(collection).

The shortcoming of that is that there is no dispatch to the correct module for that datatype.  You can't just do length(Data), you'd have to explicitly know to call queue:length(Data) or set:length(Data), etc.  You can't just pass around a data object because that doesn't indicate which module's functions to use on it.  I could see a similar packaging to records being used:

Queue module returns {queue, [Data]}, stack module returns {stack, [Data]}, etc

and in the collection module it simply dispatches to whatever module is named in the first field:

collection:length(A = {Module, _}) -> Module:length(A) end.
collection:to_string(A = {Module, _}) -> Module:to_string(A) end.
etc

Of course, this is exactly what OO implementations do, having a vtable or type identifier embedded in each object to tell what class's methods to call when using the object.

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