From: James Gray <james@...>
Date: 2009-04-29T21:39:40+09:00
Subject: Re: Hash#map

On Apr 29, 2009, at 1:00 AM, Fredrik wrote:

> Is there any good reason why Hash#map does not give back a Hash (Ruby
> 1.8 but same in 1.9 as far as I know)?

It wouldn't make sense for Hash#map to return a Hash since you are not  
required to transform it into key-value pairs:

 >> {1 => "one", 2 => "two"}.map { |k, v| "#{k} is #{v}" }
=> ["1 is one", "2 is two"]

> I often find myself writing
> these kind of things:
>
> newhash = oldhash.inject({}) { |h,(k,v)| h[k] = some_operation(v); h }

1.9 adds each_with_object() for this very usage.  You don't want the  
return value of the block to carry forward, but instead the object you  
started with.  That's what each_with_object() does.  So your code  
becomes the following in Ruby 1.9:

newhash = oldhash.each_with_object({}) { |(k, v), h|
   h[k] = some_operation(v)
}

Hope that helps.

James Edward Gray II