From: Shashank Date <sdate@...>
Date: 2005-03-15T22:59:01+09:00
Subject: Re: YAML obj merging

Hi Florian,

Florian Gross wrote:

<snip>

> class Hash
>   # Similar to Hash#merge, but this version works recursively so that
>   # nested Hashs will be merged as well. You can specify a collision
>   # block which will be invoked for conflicting items. (It takes the
>   # same argument list as the collision block supplied to Hash#merge:
>    |hash, item1, item2|)

I am not able to understand how the collision block thing will work 
here. Can you please give an example? I tried this, but it did not work 
like I expected:

b.mix(a){|key,old,nu| old} #=> {"A"=>{"B1"=>"b", "A1"=>"a"}}

>   #
>   # Usage example:
>   #   a = { "A" => { "A1" => "a" } }
>   #   b = { "A" => { "B1" => "b" } }
>   #   b.mix(a) # => {"A" => {"A1" => "a", "B1" => "b" }}
>   def mix(other, &collision_block)
>     merge_block = lambda do |hash, item1, item2|
>       if item1.is_a?(Hash) and item2.is_a?(Hash) then
>         item1.merge(item2, &merge_block)
>       elsif collision_block then

When does this elsif get executed?

>         collision_block.call(hash, item1, item2)
>       else
>         item2
>       end
>     end
> 
>     self.merge(other, &merge_block)
>   end
> end
> 
> So basically the block that Hash#merge can take is insanely useful. I've 
> also used for just detecting Hash collisions in the past as well.

I did not know that Hash#merge could take a block. Thanks for pointing 
it out.

-- shanko