[erlang-questions] Newbie question: avoiding massive 'case' statement

[Michael McDaniel]

maybe something like or a variation of  ...

 TransactionType = "ZABC" ,  %% or however it gets loaded
 Request = "some appropriate request for TransactionType" ,

 TT = string:to_lower(TransactionType) ,  %% no problem if already lower


 erlang:apply( erlang:list_to_atom(TT), process_request, [Request] ) ,


 %% and catch the exception from the apply 


~Michael


On Thu, Mar 06, 2008 at 07:59:05AM +1100, David Mitchell wrote:
> Hello everyone,
> 
> Newbie alert...
> 
> I've got a block of code that looks like:
> 
> case TransactionType of
>   "ZABC" ->
>     zabc:process_request(Request);
>   "Z123" ->
>     z123:process_request(Request);
>   "YPQX" ->
>     ypqx:process_request(Request);
> ...
>   TransactionType ->
>     error_logger:info_msg("Unknown transaction type")
> end
> 
> This is all fine and dandy, but I'm expecting the 'case' statement to
> grow to handle several hundred different values of TransactionType
> over time.  The code is going to get unwieldy in size, and the
> likelihood of mistakes in cut/paste updating of the 'case' block is
> going to get pretty high.
> 
> As an alternative to the above, is there a way to do something like
> 
> try
>   &&&TransactionType&&&:process_request(Request)
> catch
>   error_logger:info_msg("Unknown transaction type")
> end
> 
> where &&&TransactionType&&&:process_request(...) is some "magic code"
> that lets me call the process_request function in the module that has
> the name of the value of TransactionType  (hopefully that's clear, if
> not necessarily English)?
> 
> Alternately, is there some sort of refactoring I could do to avoid the
> massive 'case' statement?
> 
> There may be some obvious solution to do this, but I haven't been able
> to find it...
> 
> Thanks in advance
> 
> Dave Mitchell
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-- 
Michael McDaniel
Portland, Oregon, USA
http://autosys.us
+1 503 283 5284