Enumerable#sum without blocks. Closes #5505. Don't assume 0 identity for sum.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4495 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activesupport/CHANGELOG

 *SVN*
 
-* Added Enumerable#sum for calculating a sum from the elements [DHH]. Examples:
+* Added Enumerable#sum for calculating a sum from the elements [DHH, jonathan@daikini.com]. Examples:
 
+    [1, 2, 3].sum
     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]

activesupport/lib/active_support/core_ext/enumerable.rb

@@ -26,11 +26,18 @@ def group_by
   #  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) }
+  # This is instead of payments.inject { |sum, p| sum + p.price }
+  #
+  # Also calculates sums without the use of a block:
+  #   [5, 15, 10].sum # => 30
+  def sum(&block)
+    if block_given?
+      map(&block).sum
+    else
+      inject { |sum, element| sum + element }
+    end
   end
-  
+
   # Convert an enumerable to a hash. Examples:
   # 
   #   people.index_by(&:login)
@@ -45,4 +52,4 @@ def index_by
     end
   end
   
-end
\ No newline at end of file
+end

activesupport/test/core_ext/enumerable_test.rb

@@ -3,6 +3,9 @@
 require File.dirname(__FILE__) + '/../../lib/active_support/core_ext/enumerable'
 
 Payment = Struct.new(:price)
+class SummablePayment < Payment
+  def +(p) self.class.new(price + p.price) end
+end
 
 class EnumerableTests < Test::Unit::TestCase
   def test_group_by
@@ -19,13 +22,31 @@ def test_group_by
       assert group.all? {|person| person.name == name}
     end
   end
-  
+
   def test_sums
+    assert_equal 30, [5, 15, 10].sum
+    assert_equal 30, [5, 15, 10].sum { |i| i }
+
+    assert_equal 'abc', %w(a b c).sum
+    assert_equal 'abc', %w(a b c).sum { |i| i }
+
     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 }
+
+    payments = [ SummablePayment.new(5), SummablePayment.new(15) ]
+    assert_equal SummablePayment.new(20), payments.sum
+    assert_equal SummablePayment.new(20), payments.sum { |p| p }
   end
-  
+
+  def test_nil_sums
+    assert_raise(TypeError) { [5, 15, nil].sum }
+
+    payments = [ Payment.new(5), Payment.new(15), Payment.new(10), Payment.new(nil) ]
+    assert_raise(TypeError) { payments.sum(&:price) }
+    assert_equal 60, payments.sum { |p| p.price.to_i * 2 }
+  end
+
   def test_index_by
     payments = [ Payment.new(5), Payment.new(15), Payment.new(10) ]
     assert_equal(
@@ -33,5 +54,4 @@ def test_index_by
       payments.index_by(&:price)
     )
   end
-  
 end