From: Robert Dober <robert.dober@...>
Date: 2009-08-14T17:04:26+09:00
Subject: Re: Simple If

On Fri, Aug 14, 2009 at 9:02 AM, Robert
Klemme<shortcutter@googlemail.com> wrote:
> 2009/8/13 Robert Dober <robert.dober@gmail.com>:
>> On Thu, Aug 13, 2009 at 5:00 PM, Robert
>> Klemme<shortcutter@googlemail.com> wrote:
>>> 2009/8/13 Robert Dober <robert.dober@gmail.com>:
>>>> On Thu, Aug 13, 2009 at 10:18 AM, Anthony Eden<anthonyeden@gmail.com> wrote:
>>>>> On Wed, Aug 12, 2009 at 10:14 PM, Pete Moran<pete@zoborg.com> wrote:
>>>>>> UPDATE:
>>>>>>
>>>>>> This works
>>>>>>
>>>>>>    if params[:country][:id]
>>>>>>      id = params[:country][:id]
>>>>>>    else
>>>>>>      id = params[:id]
>>>>>>    end
>>>>>>
>>>>>> But is there a oneliner equivalent?
>>>>>
>>>>> id = params[:country][:id] || params[:id]
>>>> maybe safer but still not safe
>>>>
>>>> id = params[:country] && params[:country][:id] || params[:id]
>>>
>>> I'd go for
>>>
>>> id = (params[:country] || params)[:id]
>> that is nicely refactored
>>>
>>> But, this does not seem to be what OP needs.  The Perl code was
>>>
>>> my $id = (exists $hash->{id}) ? $hash->{id} : $_;
>>>
>>> For me that translates to something like this:
>>>
>>> def any_method(some_id_argument)
>>>  id = @hash[:id] || some_id_argument
>> not really, rather
>>   id = @hash.fetch( :id, some_id_argument)
>
> Good point!  Even though I brought up Hash#fetch in a recent thread I
> forgot it this time.  Darn, my memory... :-)
>
>> or the fancier
>>   id = @hash.fetch( :id ){ some_id_argument }
>>
>> just for completeness ;) of the API. (This is interesting for some use
>> cases as e.g. throwing an exception in the block, thus
>>
>> begin
>>  @hash.fetch( :id )
>> rescue KeyNotFoundIBelieve
>>   raise OMGWhatDidYouDo
>> end
>>
>> becomes
>>
>> @hash.fetch( :id ){ raise OMGWhatDidYouDo, "<b>AGAIN</b>" } ;)
>
> If that should be general behavior then I'd do
>
> @hash = Hash.new { raise OMGWhatDidYouDo, "<b>AGAIN</b>" }
>
> elsewhere and then just
>
> id = @hash[:id]
>
> It depends on whether you want the same behavior for all misses or just some.
Right, i.e. a hash implementing parameters will have varying behavior,
depending if the parameter is optional or not.
Maybe we want to add a messgae about the violating key, so elaborate
the useful Hash::new pattern for those who are not familiar with it:

@h = Hash::new{ |_, k| raise OMGDidYouForgetToSetThisKey, "violating key #{k}" }

R.