Argument more strictly

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

@@ -215,13 +215,15 @@ def sort_by(&block)
   # Returns the first element, or the first +n+ elements, of the enumerable.
   # If the enumerable is empty, the first form returns <code>nil</code>, and the
   # second form returns an empty array.
-  def first(n=NONE)
-    if n == NONE
+  def first(*args)
+    case args.length
+    when 0
       self.each do |*val|
         return val.__svalue
       end
       return nil
-    else
+    when 1
+      n = args[0]
       raise TypeError, "no implicit conversion of #{n.class} into Integer" unless n.respond_to?(:to_int)
       i = n.to_int
       raise ArgumentError, "attempt to take negative size" if i < 0
@@ -233,6 +235,8 @@ def first(n=NONE)
         break if i == 0
       end
       ary
+    else
+      raise ArgumentError, "wrong number of arguments (given #{args.length}, expected 0..1)"
     end
   end