From: Love U Ruby <lists@...>
Date: 2013-05-19T18:03:44+09:00
Subject: Need help to understand the Enumerable methods

I am very eager to know about the Enum#sort{|a,b|..}

http://www.ruby-doc.org/core-2.0/Enumerable.html#method-i-sort

Now my question is about the internal mechanism.

***Returns an array containing the items in enum sorted, either
according to their own <=> method, or by using the results of the
supplied block. The block should return -1, 0, or +1 depending on the
comparison between a and b.**

I took the below as an example:

dogs = [
  { name: "Rover", gender: "Male" },
  { name: "Max", gender: "Male" },
  { name: "Fluffy", gender: "Female" },
  { name: "Cocoa", gender: "Female" }
]

# gender asc, name asc
p(dogs.sort do |a, b|
  [a[:gender], a[:name]] <=> [b[:gender], b[:name]]
end)
#=> [{:name=>"Cocoa", :gender=>"Female"}, {:name=>"Fluffy",
:gender=>"Female"}, {:name=>"Max", :gender=>"Male"}, {:name=>"Rover",
:gender=>"Male"}]

My question is using the method `<=>` returns value `-1,0,+1`,how the
method sorting the source array ? What the things are actually going on
with the result of `<=>`?

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