add Enumerable#sort_by

mrbgems/mruby-enum-ext/mrblib/enum.rb

@@ -161,6 +161,27 @@ module Enumerable
     h
   end
 
+  ##
+  # call-seq:
+  #    enum.sort_by { |obj| block }   -> array
+  #
+  # Sorts <i>enum</i> using a set of keys generated by mapping the
+  # values in <i>enum</i> through the given block.
+  def sort_by(&block)
+    ary = []
+    orig = [] 
+    self.each_with_index{|e, i|
+      orig.push(e)
+      ary.push([block.call(e), i])
+    }
+    if ary.size > 1
+      __sort_sub__(ary, ::Array.new(ary.size), 0, 0, ary.size - 1) do |a,b|
+        a <=> b
+      end
+    end
+    ary.collect{|e,i| orig[i]}
+  end
+
   NONE = Object.new
   ##
   # call-seq:

mrblib/enum.rb

@@ -390,7 +390,7 @@ module Enumerable
   def sort(&block)
     ary = []
     self.each{|*val| ary.push(val.__svalue)}
-    unless ary.empty?
+    if ary.size > 1
       __sort_sub__(ary, ::Array.new(ary.size), 0, 0, ary.size - 1, &block)
     end
     ary