Added Enumerable#sum for calculating a sum from the elements [DHH]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4489 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/CHANGELOG

@@ -1,5 +1,12 @@
 *SVN*
 
+* Added Enumerable#sum for calculating a sum from the elements [DHH]. Examples:
+
+    payments.sum { |p| p.price * p.tax_rate }
+    payments.sum(&:price)
+  
+  This is instead of payments.inject(0) { |sum, p| sum + p.price }
+
 * Correct and clarify Array#to_sentence docs.  #5458 [brad@madriska.com]
 
 * alias_method_chain preserves method punctuation so foo, foo?, and foo! may be chained with the same feature. [Jeremy Kemper]

activesupport/lib/active_support/core_ext/enumerable.rb

@@ -1,3 +1,5 @@
+require File.dirname(__FILE__) + '/enumerable/injections'
+
 module Enumerable #:nodoc:
   # Collect an enumerable into sets, grouped by the result of a block. Useful,
   # for example, for grouping records by date.
@@ -20,4 +22,14 @@ module Enumerable #:nodoc:
       groups
     end
   end 
-end
+
+  # Calculates a sum from the elements. Examples:
+  #
+  #  payments.sum { |p| p.price * p.tax_rate }
+  #  payments.sum(&:price)
+  #
+  # This is instead of payments.inject(0) { |sum, p| sum + p.price }
+  def sum
+    inject(0) { |sum, element| sum + yield(element) }
+  end
+end

activesupport/test/core_ext/enumerable_test.rb

@@ -1,8 +1,9 @@
 require 'test/unit'
 require File.dirname(__FILE__) + '/../../lib/active_support/core_ext/enumerable'
 
+Payment = Struct.new(:price)
+
 class EnumerableTests < Test::Unit::TestCase
-  
   def test_group_by
     names = %w(marcel sam david jeremy)
     klass = Class.new
@@ -17,4 +18,10 @@ class EnumerableTests < Test::Unit::TestCase
       assert group.all? {|person| person.name == name}
     end
   end
+  
+  def test_sums
+    payments = [ Payment.new(5), Payment.new(15), Payment.new(10) ]
+    assert_equal 30, payments.sum(&:price)
+    assert_equal 60, payments.sum { |p| p.price * 2 }
+  end
 end