From fd0eaaa407fb8fd704967be2734c1b094ac630d9 Mon Sep 17 00:00:00 2001
From: David Heinemeier Hansson <david@loudthinking.com>
Date: Sat, 24 Jun 2006 16:14:59 +0000
Subject: 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                                 |  7 +++++++
 activesupport/lib/active_support/core_ext/enumerable.rb | 14 +++++++++++++-
 activesupport/test/core_ext/enumerable_test.rb          |  9 ++++++++-
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index 092c42ed3f..ed820edd73 100644
--- a/activesupport/CHANGELOG
+++ b/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]
diff --git a/activesupport/lib/active_support/core_ext/enumerable.rb b/activesupport/lib/active_support/core_ext/enumerable.rb
index 5c556ff98d..4de520f4ed 100644
--- a/activesupport/lib/active_support/core_ext/enumerable.rb
+++ b/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
\ No newline at end of file
diff --git a/activesupport/test/core_ext/enumerable_test.rb b/activesupport/test/core_ext/enumerable_test.rb
index df14200e42..882111cd79 100644
--- a/activesupport/test/core_ext/enumerable_test.rb
+++ b/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
-- 
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