Add support for Array mutations

README.md

@@ -310,8 +310,10 @@ user.attributes
 
 ### IMPORTANT note about member coercions
 
-ShallowAttributes performs coercions only when a value is being assigned. If you mutate the value
-later on using its own interfaces then coercion won't be triggered.
+ShallowAttributes guarantee coercions only when a value is being assigned. If you mutate the value
+later on using its own interfaces then coercion may not be triggered.
+
+But ShallowAttributes uses `MutableArray < Array` with redefined mutation methods for `Array`s.
 
 Here's an example:
 
@@ -331,7 +333,7 @@ library = Library.new
 # This will coerce Hash to a Book instance
 library.books = [ { :title => 'Introduction' } ]
 
-# This WILL NOT COERCE the value because you mutate the books array with Array#<<
+# This WILL COERCE the value because ShallowAttributes uses `MutableArray < Array` with redefined `#<<`
 library.books << { :title => 'Another Introduction' }
 ```
 

lib/shallow_attributes/class_methods.rb

@@ -84,7 +84,7 @@ def attributes
     #
     # @since 0.1.0
     def attribute(name, type, options = {})
-      options[:default] ||= [] if type == Array
+      options[:default] ||= Type::MutableArray.new if type == Array
 
       default_values[name] = options.delete(:default)
       mandatory_attributes[name] = options.delete(:present)

lib/shallow_attributes/type.rb

@@ -1,4 +1,5 @@
 require 'shallow_attributes/type/array'
+require 'shallow_attributes/type/mutable_array'
 require 'shallow_attributes/type/boolean'
 require 'shallow_attributes/type/date_time'
 require 'shallow_attributes/type/float'

lib/shallow_attributes/type/array.rb

@@ -27,16 +27,7 @@ def coerce(values, options = {})
         unless values.is_a? ::Array
           raise ShallowAttributes::Type::InvalidValueError, %(Invalid value "#{values}" for type "Array")
         end
-        values.map! do |value|
-          ShallowAttributes::Type.coerce(item_klass(options[:of]), value)
-        end
-      end
-
-      private
-
-      def item_klass(klass)
-        return klass unless klass.is_a? ::String
-        Object.const_get(klass)
+        MutableArray.new(values, **options)
       end
     end
   end

lib/shallow_attributes/type/mutable_array.rb

@@ -0,0 +1,46 @@
+module ShallowAttributes
+  module Type
+    # Class for mutable arrays.
+    #
+    # @abstract
+    #
+    # @since 0.9.1
+    class MutableArray < ::Array
+      def initialize(items = [], of: nil)
+        @of = of
+        super(
+          items.map { |item| ShallowAttributes::Type.coerce(item_class, item) }
+        )
+      end
+
+      def <<(item)
+        super ShallowAttributes::Type.coerce(item_class, item)
+      end
+
+      def push(*items)
+        super(
+          *items.map { |item| ShallowAttributes::Type.coerce(item_class, item) }
+        )
+      end
+
+      def concat(other)
+        super(
+          other.map { |item| ShallowAttributes::Type.coerce(item_class, item) }
+        )
+      end
+
+      def replace(other)
+        super(
+          other.map { |item| ShallowAttributes::Type.coerce(item_class, item) }
+        )
+      end
+
+      private
+
+      def item_class
+        return @of unless @of.is_a? ::String
+        Object.const_get(@of)
+      end
+    end
+  end
+end

test/custom_types_test.rb

@@ -105,6 +105,64 @@ class Person
         person.addresses[0].must_be_instance_of Address
       end
 
+      describe 'change array by embedded values' do
+        it 'works for #<<' do
+          person.addresses << { street: 'Street 4/2', city: { name: 'Berlin' } }
+
+          person.addresses.must_be_kind_of Array
+          person.addresses[2].must_be_instance_of Address
+
+          person.addresses[2].street.must_be_instance_of String
+          person.addresses[2].street.must_equal 'Street 4/2'
+
+          person.addresses[2].city.must_be_instance_of City
+          person.addresses[2].city.name.must_equal 'Berlin'
+        end
+
+        it 'works for #push' do
+          person.addresses.push street: 'Street 4/2', city: { name: 'Berlin' }
+
+          person.addresses.must_be_kind_of Array
+          person.addresses[2].must_be_instance_of Address
+
+          person.addresses[2].street.must_be_instance_of String
+          person.addresses[2].street.must_equal 'Street 4/2'
+
+          person.addresses[2].city.must_be_instance_of City
+          person.addresses[2].city.name.must_equal 'Berlin'
+        end
+
+        it 'works for #concat' do
+          person.addresses.concat [
+            { street: 'Street 4/2', city: { name: 'Berlin' } }
+          ]
+
+          person.addresses.must_be_kind_of Array
+          person.addresses[2].must_be_instance_of Address
+
+          person.addresses[2].street.must_be_instance_of String
+          person.addresses[2].street.must_equal 'Street 4/2'
+
+          person.addresses[2].city.must_be_instance_of City
+          person.addresses[2].city.name.must_equal 'Berlin'
+        end
+
+        it 'works for #replace' do
+          person.addresses.replace [
+            { street: 'Street 4/2', city: { name: 'Berlin' } }
+          ]
+
+          person.addresses.must_be_kind_of Array
+          person.addresses[0].must_be_instance_of Address
+
+          person.addresses[0].street.must_be_instance_of String
+          person.addresses[0].street.must_equal 'Street 4/2'
+
+          person.addresses[0].city.must_be_instance_of City
+          person.addresses[0].city.name.must_equal 'Berlin'
+        end
+      end
+
       describe '#attributes' do
         it 'returns attributes hash' do
           hash = person.attributes