arraywithfinders.rb

# 
# Implements the ArrayWithFinders class, that adds
# finders with names similar to ActiveRecord's ones:
# 
# * find_by_XYZ     -> calls the `XYZ` method on the array items,
#                      returing the first one on which the method
#                      didn't return nil/false
# * find_all_by_XYZ -> calls the `XYZ` method on the array items,
#                      returing all the ones on whose the method
#                      didn't return nil/false
# * remove_by_XXX   -> removes *all* the elements whose XXX method
#                      returns true. Caveat: this finder is aliased
#                      as remove_all_by_XXX
#
# (C) 2008 ~ Marcello Barnaba <vjt@openssl.it>.
# Released under the terms of the Ruby License.
# 

class ArrayWithFinders < Array
  def method_missing(meth, *args, &block)
    if meth.to_s =~ /^(find|remove)_(all_)?by_(\w+)/
      if args.size != 1
        raise ArgumentError, "wrong number of arguments (#{args.size} for 1)"
      end

      if $1 == 'find'
        meth = $2.nil? ? :find : :select
      else
        meth = :reject!
      end

      attr = $3.to_sym
      key = args.first

      self.send(meth) { |b| b.send(attr) == key }
    else
      super(meth, *args, &block)
    end
  end
end

if $0 == __FILE__
  require 'test/unit'

  class ArrayTest < Test::Unit::TestCase
    def test_finders
      populate
      index = rand Size
      assert_equal(Item.new(index), @ary.find_by_foo(index))
    end

    def test_exception
      populate
      assert_raise(NoMethodError) { @ary.find_by_bar(42) }
      assert_raise(ArgumentError) { @ary.find_by_foo }
      assert_raise(ArgumentError) { @ary.find_by_foo(1,2,3) }
    end

    private
    Item = Struct.new(:foo)
    Size = 10
    def populate
      @ary = ArrayWithFinders.new((0..Size).map { |i| Item.new(i) })
    end
  end
end