Hash#shift

Ruby
1

Hi,

I was reading this
http://www.rubycentral.com/book/ref_c_hash.html#Hash.shift

and I wondered how this could be useful. I must be missing something.

I tried this

ahash = {“a” => “apple”,“b”=> “boat”,“c” =>“car”, “dog” => “zebra”,
“elephant” => “yak”}
p ahash #=>{“a” => “apple”,“b”=> “boat”,“c” =>“car”,“elephant” =>
“yak”, “dog” => “zebra”}
p ahash.shift #=>[“a”, “apple”]
p ahash.shift #=>[“b”, “boat”]
p ahash.shift #=>[“c”, “car”]
p ahash.shift #=>[“elephant”, “yak”]
p ahash.shift #=>[“dog”, “zebra”]

Since the order of a hash is not guaranteed, you do not know what you
are shifting at any given time. Is this right?
If you just wanted to shift everything you could use Hash#each.

What am I missing?

Harry

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2

On 14.05.2007 14:59, Harry K. wrote:

“elephant” => “yak”}
If you just wanted to shift everything you could use Hash#each.

What am I missing?

I never had use for this myself but it might be useful in cases where
you want to iterate through a (possibly temporary) Hash and make sure
that elements that you have processed are removed. Like

h={:foo=>1, :bar=>2, :baz=>3}
=> {:baz=>3, :foo=>1, :bar=>2}

until h.empty?
k, v = h.shift
puts “processing: #{k} - #{v}”
end
processing: baz - 3
processing: foo - 1
processing: bar - 2
=> nil

h
=> {}

If you now leave the loop early (for whatever reasons, “return” or
raise) you only leave elements that still have to be processed in the
Hash.

Kind regards

robert

3

On 5/14/07, Robert K. [email protected] wrote:

processing: baz - 3

    robert

OK.
You would be shifting in a somewhat random order but you would be able
to keep track of what had not yet been shifted.

Thanks for that example.

Harry

–

A Look into Japanese Ruby List in English
http://www.kakueki.com/