Support --no- prefix for inverting boolean options

closes #168

2 files changed, 21 insertions, 2 deletions

diff --git a/lib/slop/parser.rb b/lib/slop/parser.rb
index 70994a7..1bfa134 100644
--- a/lib/slop/parser.rb
+++ b/lib/slop/parser.rb
@@ -92,6 +92,8 @@ module Slop
     def try_process(flag, arg)
       if option = matching_option(flag)
         process(option, arg)
+      elsif flag.start_with?("--no-") && option = matching_option(flag.sub("no-", ""))
+        process(option, false)
       elsif flag =~ /\A-[^-]/ && flag.size > 2
         # try and process as a set of grouped short flags. drop(1) removes
         # the prefixed -, then we add them back to each flag separately.
diff --git a/lib/slop/types.rb b/lib/slop/types.rb
index ad7461c..672aef3 100644
--- a/lib/slop/types.rb
+++ b/lib/slop/types.rb
@@ -8,12 +8,29 @@ module Slop
 
   # Cast the option argument to true or false.
   # Override default_value to default to false instead of nil.
-  # This option type does not expect an argument.
+  # This option type does not expect an argument. However, the API
+  # supports value being passed. This is to ensure it can capture
+  # an explicit false value
   class BoolOption < Option
-    def call(_value)
+    attr_accessor :explicit_value
+
+    def call(value)
+      self.explicit_value = value
       true
     end
 
+    def value
+      if force_false?
+        false
+      else
+        super
+      end
+    end
+
+    def force_false?
+      explicit_value == false
+    end
+
     def default_value
       config[:default] || false
     end