Added Object#presence that returns the object if it's #present? other…

…wise returns nil [DHH/Colin Kelley]

activesupport/CHANGELOG

@@ -1,5 +1,7 @@
 *Edge*
 
+* Added Object#presence that returns the object if it's #present? otherwise returns nil [DHH/Colin Kelley]
+
 * Add Enumerable#exclude? to bring parity to Enumerable#include? and avoid if !x.include?/else calls [DHH]
 
 * Update Edinburgh TimeZone to use "Europe/London" instead of "Europe/Dublin" #3310 [Phil Ross]

activesupport/lib/active_support/core_ext/object/blank.rb

@@ -2,11 +2,11 @@ class Object
   # An object is blank if it's false, empty, or a whitespace string.
   # For example, "", "   ", +nil+, [], and {} are blank.
   #
-  # This simplifies
+  # This simplifies:
   #
   #   if !address.nil? && !address.empty?
   #
-  # to
+  # ...to:
   #
   #   if !address.blank?
   def blank?
@@ -17,6 +17,24 @@ def blank?
   def present?
     !blank?
   end
+
+  # Returns object if it's #present? otherwise returns nil.
+  # object.presence is equivalent to object.present? ? object : nil.
+  #
+  # This is handy for any representation of objects where blank is the same
+  # as not present at all.  For example, this simplifies a common check for
+  # HTTP POST/query parameters:
+  #
+  #   state   = params[:state]   if params[:state].present?
+  #   country = params[:country] if params[:country].present?
+  #   region  = state || country || 'US'
+  #
+  # ...becomes:
+  #
+  #   region = params[:state].presence || params[:country].presence || 'US'
+  def presence
+    self if present?
+  end
 end
 
 class NilClass #:nodoc:

activesupport/test/core_ext/blank_test.rb

@@ -14,12 +14,17 @@ class BlankTest < Test::Unit::TestCase
   NOT   = [ EmptyFalse.new, Object.new, true, 0, 1, 'a', [nil], { nil => 0 } ]
 
   def test_blank
-    BLANK.each { |v| assert v.blank?, "#{v.inspect} should be blank" }
+    BLANK.each { |v| assert v.blank?,  "#{v.inspect} should be blank" }
     NOT.each   { |v| assert !v.blank?, "#{v.inspect} should not be blank" }
   end
 
   def test_present
     BLANK.each { |v| assert !v.present?, "#{v.inspect} should not be present" }
-    NOT.each   { |v| assert v.present?, "#{v.inspect} should be present" }
+    NOT.each   { |v| assert v.present?,  "#{v.inspect} should be present" }
+  end
+
+  def test_presence
+    BLANK.each { |v| assert_equal nil, v.presence, "#{v.inspect}.presence should return nil" }
+    NOT.each   { |v| assert_equal v,   v.presence, "#{v.inspect}.presence should return self" }
   end
 end