Add Hashie::Extensions::Mash::SafeAssignment

This is part 3 of 3 of the to-do list determined in #198.

6 files changed, 57 insertions, 2 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2213263..0915810 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,8 +5,9 @@
 * [#197](https://github.com/intridea/hashie/pull/197): Dont convert keys to string on initalization of mash - [@gregory](https://github.com/gregory).
 * [#201](https://github.com/intridea/hashie/pull/201): Hashie::Trash transforms can be inherited - [@fobocaster](https://github.com/fobocaster).
 * [#189](https://github.com/intridea/hashie/pull/189): Added Rash#fetch - [@medcat](https://github.com/medcat).
-* [#204](https://github.com/intridea/hashie/pull/204): Added Hashie::Extensions::MethodOverridingWriter and Hashie::Extensions::MethodAccessWithOverride - [@michaelherold](https://github.com/michaelherold).
 * [#200](https://github.com/intridea/hashie/pull/200): Improved coercion: primitives and error handling - [@maxlinc](https://github.com/maxlinc).
+* [#204](https://github.com/intridea/hashie/pull/204): Added Hashie::Extensions::MethodOverridingWriter and Hashie::Extensions::MethodAccessWithOverride - [@michaelherold](https://github.com/michaelherold).
+* [#205](http://github.com/intridea/hashie/pull/205): Added Hashie::Extensions::Mash::SafeAssignment - [@michaelherold](https://github.com/michaelherold).
 * Your contribution here.
 
 ## 3.2.0 (7/10/2014)
diff --git a/README.md b/README.md
index 82b59ae..d47fecb 100644
--- a/README.md
+++ b/README.md
@@ -342,6 +342,21 @@ mash = Mash.load('data/user.csv', parser: MyCustomCsvParser)
 mash[1] #=> { name: 'John', lastname: 'Doe' }
 ```
 
+### Mash Extension: SafeAssignment
+
+This extension can be mixed into a Mash to guard the attempted overwriting of methods by property setters. When mixed in, the Mash will raise an `ArgumentError` if you attempt to write a property with the same name as an existing method.
+
+#### Example:
+
+```ruby
+class SafeMash < ::Hashie::Mash
+  include Hashie::Extensions::Mash::SafeAssignment
+end
+
+safe_mash = SafeMash.new
+safe_mash.zip = 'Test' # => ArgumentError
+```
+
 ## Dash
 
 Dash is an extended Hash that has a discrete set of defined properties and only those properties may be set on the hash. Additionally, you can set defaults for each property. You can also flag a property as required. Required properties will raise an exception if unset.
diff --git a/lib/hashie.rb b/lib/hashie.rb
index 40a1af1..2cc24dd 100644
--- a/lib/hashie.rb
+++ b/lib/hashie.rb
@@ -31,5 +31,9 @@ module Hashie
     module Dash
       autoload :IndifferentAccess, 'hashie/extensions/dash/indifferent_access'
     end
+
+    module Mash
+      autoload :SafeAssignment, 'hashie/extensions/mash/safe_assignment'
+    end
   end
 end
diff --git a/lib/hashie/extensions/mash/safe_assignment.rb b/lib/hashie/extensions/mash/safe_assignment.rb
new file mode 100644
index 0000000..2afedc5
--- /dev/null
+++ b/lib/hashie/extensions/mash/safe_assignment.rb
@@ -0,0 +1,13 @@
+module Hashie
+  module Extensions
+    module Mash
+      module SafeAssignment
+        def assign_property(name, value)
+          fail ArgumentError, "The property #{name} clashes with an existing method." if methods.include?(name)
+
+          self[name] = value
+        end
+      end
+    end
+  end
+end
diff --git a/lib/hashie/mash.rb b/lib/hashie/mash.rb
index 0206195..62c0564 100644
--- a/lib/hashie/mash.rb
+++ b/lib/hashie/mash.rb
@@ -160,6 +160,11 @@ module Hashie
     alias_method :update, :deep_update
     alias_method :merge!, :update
 
+    # Assigns a value to a key
+    def assign_property(name, value)
+      self[name] = value
+    end
+
     # Performs a shallow_update on a duplicate of the current mash
     def shallow_merge(other_hash)
       dup.shallow_update(other_hash)
@@ -201,7 +206,7 @@ module Hashie
       name, suffix = method_suffix(method_name)
       case suffix
       when '='
-        self[name] = args.first
+        assign_property(name, args.first)
       when '?'
         !!self[name]
       when '!'
diff --git a/spec/hashie/extensions/mash/safe_assignment_spec.rb b/spec/hashie/extensions/mash/safe_assignment_spec.rb
new file mode 100644
index 0000000..1ac8678
--- /dev/null
+++ b/spec/hashie/extensions/mash/safe_assignment_spec.rb
@@ -0,0 +1,17 @@
+require 'spec_helper'
+
+describe Hashie::Extensions::Mash::SafeAssignment do
+  class MashWithSafeAssignment < Hashie::Mash
+    include Hashie::Extensions::Mash::SafeAssignment
+  end
+
+  context 'when included in Mash' do
+    subject { MashWithSafeAssignment.new }
+
+    context 'when attempting to override a method' do
+      it 'raises an error' do
+        expect { subject.zip = 'Test' }.to raise_error(ArgumentError)
+      end
+    end
+  end
+end