From: Wybo Dekker <wybo@...>
Date: 2006-02-04T19:40:16+09:00
Subject: how to vary sort's block?

When I have an array of objects (Thing's, say) with two properties (say
`name' and `amount') I want to be able to sort that array by either of
these properties, depending on circumstances (like the value of the
variable `order').

The script below is an example, and it works, but I don't like it. 
I there a better way to do it, without an if..else construction?

For example, would it be possible to put several {|a,b|...} blocks for
the sort in a hash with keys telling what I want to sort on?

#!/usr/bin/ruby

class Thing
  attr_reader :name,:amount

  def initialize(name,amount)
    @name,@amount = name,amount
  end

  def list
    puts ['',@name,@amount].join("\t")
  end
end

class Array
  def byamount
    self.sort { |a,b| a.amount <=> b.amount }
  end
  def byname
    self.sort { |a,b| a.name <=> b.name }
  end
end

arr = [
  Thing.new('John',10),
  Thing.new('Anny',20)
]

order = :byname

puts "sorted #{order}:"
if order == :byname
  arr.sort { |a,b| a.name <=> b.name }.each { |a|
      a.list
      # much more code may occur here...
    }
elsif order == :byamount
  arr.sort { |a,b| a.amount <=> b.amount }.each { |a|
      a.list
      # much more code may occur here...
    }
else 
  raise "illegal order"
end 


-- 
Wybo