example of using the inject method

find_a_person.rb

#!/usr/bin/env ruby -w
# chmod +x inject_0001.rb

sclass = Struct.new('Person', :name, :age, :gender)

people = []
people << sclass.new("Sue", 20, 'M')
people << sclass.new("Sue", 20, 'F')
people << sclass.new("Sue", 21, 'M')
people << sclass.new("Joe", 20, 'M')

class PersonFinder

  attr_reader :people

  def initialize people
    @people = people
  end

  def find parms = {}
    parms.map do |attribute, value|
      self.public_send("find_by_#{attribute}", value)
    end.inject {|accumulated_results, results| accumulated_results & results}.first
  end

  def find_by_name name
    people.find_all {|person| person.name == name}
  end

  def find_by_age age
    people.find_all {|person| person.age == age}
  end

  def find_by_gender gender
    people.find_all {|person| person.gender == gender}
  end
end

if __FILE__ == $0
  p PersonFinder.new(people).find( {name: 'Sue', age: 20, gender: 'M'} )
end