2 files changed, 88 insertions, 2 deletions
diff --git a/mrbgems/mruby-enum-ext/mrblib/enum.rb b/mrbgems/mruby-enum-ext/mrblib/enum.rb
index d0e125850..1849ff4cd 100644
--- a/mrbgems/mruby-enum-ext/mrblib/enum.rb
+++ b/mrbgems/mruby-enum-ext/mrblib/enum.rb
@@ -267,4 +267,72 @@ module Enumerable
     ary
   end
   alias collect_concat flat_map
+
+  ##
+  # call-seq:
+  #    enum.max_by {|obj| block }      -> obj
+  #    enum.max_by                     -> an_enumerator
+  #
+  # Returns the object in <i>enum</i> that gives the maximum
+  # value from the given block.
+  #
+  # If no block is given, an enumerator is returned instead.
+  #
+  #    %w[albatross dog horse].max_by {|x| x.length }   #=> "albatross"
+
+  def max_by(&block)
+    return to_enum :max_by unless block_given?
+
+    first = true
+    max = nil
+    max_cmp = nil
+
+    self.each do |*val|
+      if first
+        max = val.__svalue
+        max_cmp = block.call(*val)
+        first = false
+      else
+        if (cmp = block.call(*val)) > max_cmp
+          max = val.__svalue
+          max_cmp = cmp
+        end
+      end
+    end
+    max
+  end
+
+  ##
+  # call-seq:
+  #    enum.min_by {|obj| block }      -> obj
+  #    enum.min_by                     -> an_enumerator
+  #
+  # Returns the object in <i>enum</i> that gives the minimum
+  # value from the given block.
+  #
+  # If no block is given, an enumerator is returned instead.
+  #
+  #    %w[albatross dog horse].min_by {|x| x.length }   #=> "dog"
+
+  def min_by(&block)
+    return to_enum :min_by unless block_given?
+
+    first = true
+    min = nil
+    min_cmp = nil
+
+    self.each do |*val|
+      if first
+        min = val.__svalue
+        min_cmp = block.call(*val)
+        first = false
+      else
+        if (cmp = block.call(*val)) < min_cmp
+          min = val.__svalue
+          min_cmp = cmp
+        end
+      end
+    end
+    min
+  end
 end
diff --git a/mrbgems/mruby-enum-ext/test/enum.rb b/mrbgems/mruby-enum-ext/test/enum.rb
index 9523b497e..ba0851582 100644
--- a/mrbgems/mruby-enum-ext/test/enum.rb
+++ b/mrbgems/mruby-enum-ext/test/enum.rb
@@ -47,11 +47,21 @@ assert("Enumerable#sort_by") do
 end
 
 assert("Enumerable#first") do
-  a = [1, 2, 3]
+  a = Object.new
+  a.extend Enumerable
+  def a.each
+    yield 1
+    yield 2
+    yield 3
+  end
   assert_equal 1, a.first
   assert_equal [1, 2], a.first(2)
   assert_equal [1, 2, 3], a.first(10)
-  assert_nil [].first
+  a = Object.new
+  a.extend Enumerable
+  def a.each
+  end
+  assert_nil a.first
 end
 
 assert("Enumerable#count") do
@@ -66,3 +76,11 @@ assert("Enumerable#flat_map") do
   assert_equal [1, -1, 2, -2, 3, -3, 4, -4], [1, 2, 3, 4].flat_map { |e| [e, -e] }
   assert_equal [1, 2, 100, 3, 4, 100], [[1, 2], [3, 4]].flat_map { |e| e + [100] }
 end
+
+assert("Enumerable#max_by") do
+  assert_equal "albatross", %w[albatross dog horse].max_by { |x| x.length }
+end
+
+assert("Enumerable#min_by") do
+  assert_equal "dog", %w[albatross dog horse].min_by { |x| x.length }
+end