Fix a bug that flag value is processed as flag

If flag value starts with "-", unknown option error is raised.

The current flag value check is "orig_arg == opt.value.to_s". There
are some objects such as Regexp and Time that input value and its #to_s
aren't same.

lib/slop/parser.rb

@@ -64,7 +64,7 @@ def parse(strings)
           if opt.expects_argument?
 
             # if we consumed the argument, remove the next pair
-            if orig_arg == opt.value.to_s
+            if consume_next_argument?(orig_flag)
               pairs.delete_at(idx + 1)
             end
 
@@ -106,6 +106,13 @@ def unused_options
 
     private
 
+    def consume_next_argument?(flag)
+      return false if /=/ === flag
+      return true if flag.start_with?("--")
+      return true if /\A-[a-zA-Z]\z/ === flag
+      false
+    end
+
     # We've found an option, process and return it
     def process(option, arg)
       option.ensure_call(arg)

test/parser_test.rb

@@ -49,6 +49,12 @@
     assert_equal(-123.987, @result[:multiple])
   end
 
+  it "parses negative float" do
+    @options.regexp "--pattern"
+    @result.parser.parse %w(--pattern -x)
+    assert_equal(/-x/, @result[:pattern])
+  end
+
   describe "parsing grouped short flags" do
     before do
       @options.bool "-q", "--quiet"