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Date: Mon, 31 Jan 2011 17:31:10 +0100
From: Michal Fojtik <mfojtik@redhat.com>
To: deltacloud-dev@incubator.apache.org
Subject: Re: [PATCH] Introduces blob metadata - Adds ability to specify
 arbitrary user metadata (KEY-VALUE) for S3, Cloudfiles and Azure, during
 blob creation
Message-ID: <20110131163110.GC5879@redhat.com>
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 <20110131092805.GB5879@redhat.com>
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On 31/01/11 18:18 +0200, marios@redhat.com wrote:
>Hi Michal, thanks for taking the time.
>
>I am confused by what the code fragment below does exactly. I *think* 
>i understand what .inject does, but the code below doesn't make sense 
>to me (or to irb it seems :) ) ; where does r come from? (I tried irb 
>and ruby debugger cos I thought I was going crazy but the code 
>doesn't work - i even thought it was a ruby version issue so i tried 
>1.8.6 AND 1.9.2 as I have come across a few 1.8/1.9 issues).
>
>Can you please explain in words what:
>
>meta_array.inject({}) { |user_meta, v| user_meta[v.first]=v.last ; r }

This will create a new Hash ({} is an alias for Hash.new), then it will
start to iterate through meta_array.

Then user_meta is variable which holds that Hash and in 'v' is stored actual
item from  'meta_array'.

Then user_meta[v.first]=v.last create a new key using first item in array
and store value from second item.

Then I made a *typo*, 'r' variable should be 'user_meta', so you return this
Hash and iterate to next item... 
I'm very sorry for that typo, it makes all this very confusing.

Very good example of how to use .inject can be found here:

http://blog.jayfields.com/2008/03/ruby-inject.html


>does? (e.g. take the meta_array two dimensional array and ... iterate 
>over the user_meta array etc etc). Out of curiosity where are you 
>getting 'ruby best practice' from (e.g. can you recommend a good 
>book/site/blog etc?)

Yes, actually it's http://rubybestpractices.com ;-) There is an article
about functional programming, which describes this.

Anyway, it's not a blocker, just small hint (I found myself .inject very
useful when I was doing some meta programming in client library. It saves
variables and lines of code (and it's better for garbage collecting)). 

   -- Michal

>On 31/01/11 11:28, Michal Fojtik wrote:
>>On 28/01/11 20:15 +0200, marios@redhat.com wrote:
>>
>>Code looks good, applied cleanly, Cucumber is happy, ACK.
>>A small, minor inline comment bellow.
>>
>>-- Michal
>>
>>>From: marios <marios@redhat.com>
>
>>>> max.to_i.times do |i| could be used here as well (but do the same job ;-)
>>
>>>+ key = params[:"meta_name#{i}"]
>>>+ key = "HTTP_X_Deltacloud_Blobmeta_#{key}"
>>>+ value = params[:"meta_value#{i}"]
>>>+ user_meta[key] = value
>>>+ end #max.each do
>>>+ else #can try to get blob_metadata from http headers
>>>+ meta_array = request.env.select{|k,v|
>>>k.match(/^HTTP[-_]X[-_]Deltacloud[-_]Blobmeta[-_]/i)}
>>>+ meta_array.each do |k,v|
>>>+ user_meta[k] = v
>>>+ end
>>
>>meta_array.inject({}) { |user_meta, v| user_meta[v.first]=v.last ; r }
>>
>>(same as above ;-) But it's a good Ruby practive to use inject if it's
>>possible.
>>
>>

-- 
--------------------------------------------------------
Michal Fojtik, mfojtik@redhat.com
Deltacloud API: http://deltacloud.org
--------------------------------------------------------