From: Rick DeNatale <rick.denatale@...>
Date: 2010-10-12T21:39:56+09:00
Subject: Re: more idiomatic way to avoid errors when calling method on variable that may be nil?

On Mon, Oct 11, 2010 at 10:59 PM, Tony Arcieri <tony.arcieri@medioh.com> wrote:
> Haskell solves the "may be nil" problem with the Maybe monad (from Haskell).
> There's many ways to implement something similar... such as implementing
> Object#maybe whose method_missing (e.g. Maybe#method_missing) proxies to the
> original object. NilClass can also implement #maybe, and always return nil.
>
> On Mon, Oct 11, 2010 at 2:05 PM, Charles Calvert <cbciv@yahoo.com> wrote:
>
>> I'm using Ruby 1.8.7 patchlevel 249
>>
>> Is there a more idiomatic way to do the following?
>>
>> var = hash[key].nil? ? nil : hash[key].downcase
>>
>> Note that if hash[key] is nil, I want nil assigned to var, so this
>> won't work:
>>
>> var = hash[key].downcase unless hash[key].nil?
>>
>> Obviously I could do this, but I'm trying to keep it on one line:
>>
>> var = hash[key]
>> var = var.downcase unless var.nil?
>>

Nobody seems to have mentioned it, I guess since this is the place for
'pure' rubyists, but Rails has the following methods:

class Object
   def try(method, *args, &block)
       send(method, *args, &block)
   end
end

class NilClass
  def try(*args)
     nil
  end
end

So with this you can write simply

   var =  hash[key].try(:downcase)

-- 
Rick DeNatale

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