From: Robert Klemme <shortcutter@...>
Date: 2008-05-09T00:17:08+09:00
Subject: Re: idiom for Hash like map...

2008/5/8 Mikel Lindsaar <raasdnil@gmail.com>:
> On Thu, May 8, 2008 at 12:51 AM, ara.t.howard <ara.t.howard@gmail.com> wrote:
>>  On May 7, 2008, at 5:18 AM, Mikel Lindsaar wrote:
>>  class Fruit
>>   def to_hash
>>     { :name => name, :price => price }
>>   end
>>  end
>>  array.each{|fruit| hash.update fruit.to_hash}
>
> Hmm.. put the responsibility back into the class.  I guess that
> actually makes the most sense.

But this approach has the drawback to create a lot of temporary
instances that are thrown away immediately.

Of course I do not know your use case but if I was building an index
I'd rather insert the object as value instead of a field.  Just for
the fun of it:

irb(main):001:0> Fruit = Struct.new :name, :price
=> Fruit
irb(main):002:0> fruits = [Fruit.new("foo",1),Fruit.new("bar",2)]
=> [#<struct Fruit name="foo", price=1>, #<struct Fruit name="bar", price=2>]
irb(main):005:0> indexes = Hash.new {|h,k| h[k]= Hash.new(&h.default_proc)}
=> {}
irb(main):006:0> fruits.each {|f| f.members.each {|m| indexes[m][f[m]]=f}}
=> [#<struct Fruit name="foo", price=1>, #<struct Fruit name="bar", price=2>]
irb(main):008:0> require 'pp'
=> true
irb(main):009:0> pp indexes
{"name"=>
  {"foo"=>#<struct Fruit name="foo", price=1>,
   "bar"=>#<struct Fruit name="bar", price=2>},
 "price"=>
  {1=>#<struct Fruit name="foo", price=1>,
   2=>#<struct Fruit name="bar", price=2>}}
=> nil

Cheers

robert

-- 
use.inject do |as, often| as.you_can - without end