Merge pull request #4258 from shuujii/extend-only-when-necessary

Extend only when necessary in `lib/mruby-core-ext.rb`

lib/mruby-core-ext.rb

@@ -18,18 +18,20 @@ class String
   end
 
   # Compatible with 1.9 on 1.8
-  def %(params)
-    if params.is_a?(Hash)
-      str = self.clone
-      params.each do |k, v|
-        str.gsub!("%{#{k}}") { v }
-      end
-      str
-    else
-      if params.is_a?(Array)
-        sprintf(self, *params)
+  unless (sprintf("%{a}", :a => 1) rescue false)
+    def %(params)
+      if params.is_a?(Hash)
+        str = self.clone
+        params.each do |k, v|
+          str.gsub!("%{#{k}}") { v }
+        end
+        str
       else
-        sprintf(self, params)
+        if params.is_a?(Array)
+          sprintf(self, *params)
+        else
+          sprintf(self, params)
+        end
       end
     end
   end
@@ -37,17 +39,21 @@ end
 
 class Symbol
   # Compatible with 1.9 on 1.8
-  def to_proc
-    proc { |obj, *args| obj.send(self, *args) }
+  unless method_defined?(:to_proc)
+    def to_proc
+      proc { |obj, *args| obj.send(self, *args) }
+    end
   end
 end
 
 module Enumerable
   # Compatible with 1.9 on 1.8
-  def each_with_object(memo)
-    return to_enum :each_with_object, memo unless block_given?
-    each { |obj| yield obj, memo }
-    memo
+  unless method_defined?(:each_with_object)
+    def each_with_object(memo)
+      return to_enum :each_with_object, memo unless block_given?
+      each { |obj| yield obj, memo }
+      memo
+    end
   end
 end