From: Michael Greenly <mgreenly@...>
Date: 2006-08-08T06:31:19+09:00
Subject: Re: How to react on nil or wrong object-type as parameter

Yochen Gutmann wrote:
> So if I do understand you all correctly, in Ruby you put the responsible 
> to the caller of a method (eg print_salary()). If you want to test that 
> method, you test it only with the proper types. The next thing would be 
> testing the method which includes the call of print_salary() if it calls 
> this methods with the wrong types of parameter. Is this right?
> 
> One problem in this concept is that if some operations might work on a 
> parameter-object and the following is not the exception is thrown when 
> the object is already modified.
> 
> class Bank
>    @invitations_to_golf
> 
>    def handle_client_well client
>       client.decrease_acoount(200)
>       client.check_portfolio
>       @invitations_to_golf.push client
>    end
> 
> end
> 
> jon_doe = LowBudgetClient.new
> big_boss = VeryRichClient.new
> big_money = Bank.new
> 
> big_money.handle_client_well big_boss
> big_money.handle_client_well jon_doe // poor guy has no portfolio
> 
> So, when the hcw-method is called with jon_doe, he has to pay for better 
> handling but since he has no portfolio the exception is thrown before he 
> is entering the golf course.
> 
> One solution might be a exception around the method-body (yes, again 
> ;-)) and a include an ensure to increase the account again if something 
> broke. But again, this procedure would fail if there are many modifing 
> operations.
> 
> Perhaps I am still thinking too Java'ish and these are high theorectical 
> problems or I still dont get it.
> 
> Yochen

Is it by design that you intend to call handle_client with objects that 
don't have portfolios?  Then you need to either check for that in 
handle_clients or expect the exception and catch it where it's called.

If you didn't intend to call handl_client with a non-portfolio baring 
client than the best thing that can happen is raising an expcetion

I'm not really sure I get the conflict you were trying to get to?

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