Hash.collect

ruby-talk
1

collect seems to work on a hash:

h = {'a'=>'1', 'b'=>'2'}

params = h.collect {|k, v| "#{k}=#{v}"}.join('&')

Yet collect isn't listed as a method of hash:
http://www.ruby-doc.org/core

Is it undocumented, or is some magic going on behind the scenes -- such
as the hash getting converted to an array?

Thanks,
Joe

···

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2

Joe Ruby MUDCRAP-CE wrote:

collect seems to work on a hash:

h = {'a'=>'1', 'b'=>'2'}

params = h.collect {|k, v| "#{k}=#{v}"}.join('&')

Yet collect isn't listed as a method of hash:
RDoc Documentation

Is it undocumented, or is some magic going on behind the scenes -- such as the hash getting converted to an array?

The Hash class includes the Enumerable module, which defines #collect in terms of #each. In this case, Hash#each yields key,value pairs, so #collect does too. It doesn't get converted to an array before map is called. It does get converted to an array through the normal behavior of #map:

irb(main):003:0> h={1=>2, 3=>4}
=> {1=>2, 3=>4}
irb(main):004:0> h.map
=> [[1, 2], [3, 4]]

···

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3

Joe Ruby MUDCRAP-CE wrote:

collect seems to work on a hash:

h = {'a'=>'1', 'b'=>'2'}

params = h.collect {|k, v| "#{k}=#{v}"}.join('&')

Yet collect isn't listed as a method of hash:
RDoc Documentation

Is it undocumented, or is some magic going on behind the scenes -- such as the hash getting converted to an array?

Thanks,
Joe

No, no real magic: "collect" is part of the Enumerable module, which is mixed into Hash (and other things) and implements this functionality.

-Justin

[1]module Enumerable - RDoc Documentation

4

You might find something like the following exploratory utility useful:

def method_report(klass)
  result = klass.ancestors.inject(Array.new) do |result, anc|
    ms = (anc.instance_methods + anc.methods).sort.uniq
    result.last[1] -= ms if result.last
    result << [anc.name, ms]
  end
  result.each do |k, v|
    puts "----", k
    v.each {|m| puts "\s\s#{m}"}
  end
end
# and here's how to use it
method_report(Hash)

I'm sure there are much snazzier versions out there. m.

···

Joe Ruby MUDCRAP-CE <joeat303@yahoo.com> wrote:

collect seems to work on a hash:

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