Merge pull request #499 from michaelherold/permissive-respond-to

Add a PermissiveRespondTo extension for Mashes

2 files changed, 62 insertions, 0 deletions

diff --git a/lib/hashie.rb b/lib/hashie.rb
index a3fc11c..7f88ed4 100644
--- a/lib/hashie.rb
+++ b/lib/hashie.rb
@@ -45,6 +45,7 @@ module Hashie
 
     module Mash
       autoload :KeepOriginalKeys, 'hashie/extensions/mash/keep_original_keys'
+      autoload :PermissiveRespondTo, 'hashie/extensions/mash/permissive_respond_to'
       autoload :SafeAssignment, 'hashie/extensions/mash/safe_assignment'
       autoload :SymbolizeKeys, 'hashie/extensions/mash/symbolize_keys'
       autoload :DefineAccessors, 'hashie/extensions/mash/define_accessors'
diff --git a/lib/hashie/extensions/mash/permissive_respond_to.rb b/lib/hashie/extensions/mash/permissive_respond_to.rb
new file mode 100644
index 0000000..5f8c231
--- /dev/null
+++ b/lib/hashie/extensions/mash/permissive_respond_to.rb
@@ -0,0 +1,61 @@
+module Hashie
+  module Extensions
+    module Mash
+      # Allow a Mash to properly respond to everything
+      #
+      # By default, Mashes only say they respond to methods for keys that exist
+      # in their key set or any of the affix methods (e.g. setter, underbang,
+      # etc.). This causes issues when you try to use them within a
+      # SimpleDelegator or bind to a method for a key that is unset.
+      #
+      # This extension allows a Mash to properly respond to `respond_to?` and
+      # `method` for keys that have not yet been set. This enables full
+      # compatibility with SimpleDelegator and thunk-oriented programming.
+      #
+      # There is a trade-off with this extension: it will run slower than a
+      # regular Mash; insertions and initializations with keys run approximately
+      # 20% slower and cost approximately 19KB of memory per class that you
+      # make permissive.
+      #
+      # @api public
+      # @example Make a new, permissively responding Mash subclass
+      #   class PermissiveMash < Hashie::Mash
+      #     include Hashie::Extensions::Mash::PermissiveRespondTo
+      #   end
+      #
+      #   mash = PermissiveMash.new(a: 1)
+      #   mash.respond_to? :b  #=> true
+      module PermissiveRespondTo
+        # The Ruby hook for behavior when including the module
+        #
+        # @api private
+        # @private
+        # @return void
+        def self.included(base)
+          base.instance_variable_set :@_method_cache, base.instance_methods
+          base.define_singleton_method(:method_cache) { @_method_cache }
+        end
+
+        # The Ruby hook for determining what messages a class might respond to
+        #
+        # @api private
+        # @private
+        def respond_to_missing?(_method_name, _include_private = false)
+          true
+        end
+
+        private
+
+        # Override the Mash logging behavior to account for permissiveness
+        #
+        # @api private
+        # @private
+        def log_collision?(method_key)
+          self.class.method_cache.include?(method_key) &&
+            !self.class.disable_warnings?(method_key) &&
+            !(regular_key?(method_key) || regular_key?(method_key.to_s))
+        end
+      end
+    end
+  end
+end