`__sort_sub__` is a method defined in `Array`; fix #3970

Reorganize `__sort_sub__` arguments.

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

@@ -201,7 +201,7 @@ module Enumerable
       ary.push([block.call(e), i])
     }
     if ary.size > 1
-      __sort_sub__(ary, 0, ary.size - 1) do |a,b|
+      ary.__sort_sub__(0, ary.size - 1) do |a,b|
         a <=> b
       end
     end

mrblib/array.rb

@@ -200,28 +200,27 @@ class Array
 
   ##
   # Quick sort
-  # a     : the array to sort
   # left  : the beginning of sort region
   # right : the end of sort region
-  def __sort_sub__(a, left, right, &block)
+  def __sort_sub__(left, right, &block)
     if left < right
       i = left
       j = right
-      pivot = a[i + (j - i) / 2]
+      pivot = self[i + (j - i) / 2]
       while true
-        while ((block)? block.call(a[i], pivot): (a[i] <=> pivot)) < 0
+        while ((block)? block.call(self[i], pivot): (self[i] <=> pivot)) < 0
           i += 1
         end
-        while ((block)? block.call(pivot, a[j]): (pivot <=> a[j])) < 0
+        while ((block)? block.call(pivot, self[j]): (pivot <=> self[j])) < 0
           j -= 1
         end
         break if (i >= j)
-        tmp = a[i]; a[i] = a[j]; a[j] = tmp;
+        tmp = self[i]; self[i] = self[j]; self[j] = tmp;
         i += 1
         j -= 1
       end
-      __sort_sub__(a, left, i-1, &block)
-      __sort_sub__(a, j+1, right, &block)
+      __sort_sub__(left, i-1, &block)
+      __sort_sub__(j+1, right, &block)
     end
   end
   #  private :__sort_sub__
@@ -232,7 +231,7 @@ class Array
   def sort!(&block)
     size = self.size
     if size > 1
-      __sort_sub__(self, 0, size - 1, &block)
+      __sort_sub__(0, size - 1, &block)
     end
     self
   end