From: ara.t.howard@...
Date: 2006-02-14T06:15:14+09:00
Subject: Re: Idiomatic ruby

On Tue, 14 Feb 2006, Adam P. Jenkins wrote:

> ara.t.howard@noaa.gov wrote:
>
>>     harp:~ > cat a.rb
>>     class C
>>       def initialize(x) @x = x end
>>       def valid?()
>>         if @x == 42
>>           true
>>         else
>>           yield "x is not 42" rescue nil
>>           false
>>         end
>>       end
>>     end
>> 
>>     c = C::new 43
>>     unless c.valid?{|reason| warn "not valid : #{ reason }" }
>>       # do something
>>     end
>> 
>>     c = C::new 42
>>     c.valid?{|reason| warn "not valid : #{ reason }" }
>> 
>> 
>>     harp:~ > ruby a.rb
>>     not valid : x is not 42
>
> I like this solution the best.  Unlike the solutions involving exceptions or
> multiple return values, it still allows valid? to be used as an ordinary
> boolean function when you don't care about the reason why something's not
> valid, yet doesn't have the race conditions involved in the side-effect
> solutions.
>
> That said, I think part of the reason there's no agreed upon idiom for this
> is because it would have been more idiomatic in Ruby to not even have the
> valid? method.  Instead an exception would have been thrown as soon as the
> object became invalid, and the exception would have contained the reason.
> Having your class have a valid? method seems like how you'd design things in
> a language which doesn't have exceptions.

still - some people prefer not to do control flow with exceptions.  as with
most things, both things can be good.  i tend to use things like

   def validate!
     raise unless valid?
   end

and use either/both where it makes sense.

regards.

-a

-- 
judge your success by what you had to give up in order to get it.
- h.h. the 14th dali lama