sort_by with asc/desc

gistfile1.txt

## sortby.rb
module SortBy
  class Reverse
    include Comparable

    attr_reader :value
    def initialize(value)
      @value = value
    end
  
    def <=>(other)
      other.value <=> @value
    end
  end

  class Lazy
    def initialize(&block)
      @block = block
      @memo  = false
      @value = nil
    end
  
    def value
      @memo ? @value : (@value = @block[])
    end
  
    def <=>(other)
      value <=> other.value
    end
  end

  def asc(value=nil, &lazy)
    lazy ? SortBy::Lazy.new(&lazy) : value
  end

  def desc(value=nil, &lazy)
    value = SortBy::Lazy.new(&lazy) if lazy
    SortBy::Reverse.new(value)
  end

  module_function :asc, :desc
end

## sortby/convenience.rb
module Kernel
  def asc(value=nil, &lazy)
    lazy ? SortBy::Lazy.new(&lazy) : value
  end

  def desc(value=nil, &lazy)
    value = SortBy::Lazy.new(&lazy) if lazy
    SortBy::Reverse.new(value)
  end

  module_function :asc, :desc
end



## usage
if __FILE__ == $PROGRAM_NAME then
  require 'pp'
  Person = Struct.new(:first_name, :last_name, :age)
  people = [
    Person.new('Peter', 'Pan', 23),
    Person.new('Peter', 'Pan', 15),
    Person.new('Peter', 'Parker', 15),
  ]
  pp people.sort_by { |person| [asc(person.first_name), asc(person.last_name), desc(person.age)] }


  Foo  = Struct.new(:a, :b, :c)
  calc = proc { |s,x| sleep(s); x }
  foos = [
    Foo.new(1,2,1),
    Foo.new(1,2,2),
    Foo.new(1,3,4),
    Foo.new(2,3,4),
  ]
  start = Time.now
  pp foos.sort_by { |x| [asc(x.a), desc(calc[0.1, x.b]), asc(calc[0.2, x.c])] }
  stop = Time.now
  printf "Elapsed: %.2fs\n", stop-start

  start = Time.now
  pp foos.sort_by { |x| [asc(x.a), desc { calc[0.1, x.b] }, asc { calc[0.2, x.c] }] }
  stop = Time.now
  printf "Elapsed: %.2fs\n", stop-start

end