Fix issue #100, hashify nested types within hash maps

Co-authored-by: Brendan Weibrecht <brendan@weibrecht.net.au>

lib/dry/struct/hashify.rb

@@ -7,7 +7,7 @@ module Hashify
       # @return [Hash, Array]
       def self.[](value)
         if value.respond_to?(:to_hash)
-          value.to_hash
+          Hash[value.to_hash.map{ |k, item| [k, self[item]] }]
         elsif value.respond_to?(:to_ary)
           value.to_ary.map { |item| self[item] }
         else

spec/dry/struct_spec.rb

@@ -278,6 +278,21 @@ def obj.map
         expect(type.new.to_hash).to eq (attributes)
       end
     end
+
+    context 'on an Dry::Types::Hash.map with nested types' do
+      NestedType = Class.new(Dry::Struct::Value) do
+        attribute :age, Dry::Types['strict.integer']
+      end
+
+      type = Class.new(Dry::Struct) do
+        attribute :people, Dry::Types['hash'].map(Dry::Types['strict.string'], NestedType)
+      end
+
+      it 'hashifies the values within the hash map' do
+        attributes = { people: { 'John' => { age: 35 } } }
+        expect(type.new(attributes).to_hash).to eq(attributes)
+      end
+    end
   end
 
   describe 'pseudonamed structs' do