From: "Abinoam Jr." <abinoam@...>
Date: 2012-01-26T07:34:06+09:00
Subject: Re: A sort of design question

Panagliotis,

I think Robert Klemme is telling you to do something like this.

https://github.com/abinoam/morula/commit/40e7745c54446363b8cd32d2d05cf0cee4a70df9

Abinoam Jr.

On Wed, Jan 25, 2012 at 2:05 PM, Panagiotis Atmatzidis
<ml@convalesco.org> wrote:
> Hello,
>
> On 25 Éáí 2012, at 16:05 , Robert Klemme wrote:
>
>> On Wed, Jan 25, 2012 at 3:53 PM, Panagiotis Atmatzidis
>> <ml@convalesco.org> wrote:
>>> Dear Ladies (??) and Gentlemen (okay we have plenty of those),
>>>
>>> I wrote a script which needs a variable in order to proceed. This variable is defined by the user otherwise the default location is chosen. After a discussion I had on IRC (#ruby @ Freenode), I came up with a few questions.
>>>
>>> My script is structured like this:
>>>
>>> class [...]
>>> optparse [...]
>>> execution_flow_control [...]
>>>
>>> I do the 'control' of this variable inside the class like this:
>>>
>>> class Prog
>>>  attr_accessor :database
>>>  def initialize(database)
>>>   @database = database
>>>  end
>>>
>>> [...]
>>>        def create_table(tableid)
>>>                if @database and File.exists?(@database) <--- control
>>> [...]
>>>
>>> end
>>>
>>> I was wondering if this is the right way actually do this control since, if @database is not set, the flow will never reach that point, because the class takes 1 argument (which is @database) and if it's null, it will come up with an error.
>>
>> I do not understand what you mean by "the flow will never reach that
>> point": From what you have shown the constructor will happily accept
>> nil for parameter "database".  And if someone after that invokes
>> #create_table the code will reach just this point.  Also, I am not
>> 100% positive what you mean by "this control".
>>
>>> The script works fine, as is. I optimized it a bit, by removing and/or optimizing some functions. But I'm curious, where is the right place for doing this control which is necessary for execution?
>>
>> Considering what I see here and on github I'd say constructor of Prog
>> should check argument "database" for valid values and raise an
>> exception if nil is passed.  Then, later on, the other methods can
>> rely on this value being valid.  That's basically what OO is all
>> about: you define the valid state of an instance and maintain it
>> throughout all methods.
>
> thanks, that was the answer I was looking for.
>
>>
>> Kind regards
>>
>> robert
>>
>> --
>> remember.guy do |as, often| as.you_can - without end
>> http://blog.rubybestpractices.com/
>>
>
>
> Panagiotis Atmatzidis
> -----------------------------
> Pharmacy Student at VFU, Brno
> mailing lists: ml@convalesco.org
>
> personal info: http://www.convalesco.org
>
> The wise man said: "Never argue with an idiot, he brings you down to his level and beat you with experience."
>
>
>
>
>