From: Trans <transfire@...>
Date: 2008-10-26T21:53:40+09:00
Subject: Re: Hash.merge_add! extension - how does this code look?



On Oct 26, 7:20 am, "Greg Hauptmann" <greg.hauptmann.r...@gmail.com>
wrote:
> Hi,
> I wanted a way to be able to "add" values to a Hash such that it keeps the
> old and the new values.  For examples example adding an item to a hash for
> which the keys are dates.   Here's a first cut.  Any feedback on coding
> style etc?
>
> ================================
> class Hash
>   # Merges a hash with only one item into your hash.  If there is already a
>   # hash entry for that key the both existing value(s) & new value are kept
> via
>   # use of an Array
>   def merge_add!(h)
>     raise "Parameter passed in not a hash" if !h.instance_of?(Hash)

You don't need to do this. It is "anti-ducktyping". h could be a hash-
*like* object and that would be okay.

>     raise "Can only pass hash with one item to be added" if h.length > 1

Why artificially limit it to one entry hashes? Supporting any hash
would make it more flexible.

>     h_key = h.to_a[0][0]
>     h_value = h.to_a[0][1]
>     if self.has_key?(h_key)
>       existing_value = self[h_key]
>       existing_value_as_array = existing_value.instance_of?(Array) ?
> existing_value : [existing_value]
>       new_value = existing_value_as_array << h_value
>       self[h_key] = new_value
>     else
>       h_value.instance_of?(Array) ? self.merge!(h) : self.merge!( {h_key =>
> [h_value]} )
>     end
>   end
> end

The idea is a good one. I think implementation could use some
improvement. For comparison have a look at Facets' Hash#collate.

  http://facets.rubyforge.org/doc/api/core/classes/Hash.html#M000112

t