From: William James <w_a_x_man@...>
Date: 2007-01-21T05:10:12+09:00
Subject: Re: Proper way to either create or append to an array?


Rob Biedenharn wrote:
> On Jan 20, 2007, at 1:15 PM, Phrogz wrote:
>
> > Robert Klemme wrote:
> >> Since you're using a Hash the block constructor is the most elegant
> >> solution IMHO:
> >>
> >> def initialize
> >>    @foo = Hash.new {|h,k| h[k]=[]}
> >>    ...
> >> end
> >
> > To be clear for those unfamiliar with this: any time you ask for the
> > value of a key that doesn't exist, the block will be called (which
> > creates a new empty array). This means you can never see this
> > particular Hash has a key, since:
> >   if @foo[ :bar ]
> > will always succeed, and create a (possibly unwanted) array
> > instance in
> > the process.
>
> That's only because you're not checking for the presence of a key
> correctly:
>
>  >> myhash = Hash.new { |h,k| h[k] = Array.new }
> => {}
>  >> if myhash[:oops]
>  >>   puts "nothing"
>  >>   end
> nothing
> => nil
>  >> myhash
> => {:oops=>[]}
>  >> if myhash.has_key? :missing

I prefer to use include?, since it also works on arrays:

irb(main):006:0> ['foo','bar'].include? 'bar'
=> true