From 1170de531d358e287c6161458850a07f6521f0fd Mon Sep 17 00:00:00 2001
From: kwatch <kwatch@gmail.com>
Date: Sat, 19 Nov 2016 10:19:34 +0900
Subject: [PATCH 7/9] feat(psych): define 'Psych::Visitors::CustomClassVisitor'
 class

This new class allows user to generate custom object instead of Hash.
See document of CustomClassVisitor class for details.
---
 ext/psych/lib/psych/visitors/custom_class.rb | 84 ++++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 ext/psych/lib/psych/visitors/custom_class.rb

diff --git a/ext/psych/lib/psych/visitors/custom_class.rb b/ext/psych/lib/psych/visitors/custom_class.rb
new file mode 100644
index 0000000..313e522
--- /dev/null
+++ b/ext/psych/lib/psych/visitors/custom_class.rb
@@ -0,0 +1,84 @@
+# frozen_string_literal: false
+
+require 'psych/visitors/to_ruby'
+
+
+module Psych
+  module Visitors
+
+    ##
+    ## Visitor class to generate custom object instead of Hash.
+    ##
+    ## Example1:
+    ##
+    ##     ## define custom classes
+    ##     Team   = Struct.new('Team',   'name', 'members')
+    ##     Member = Struct.new('Member', 'name', 'gender')
+    ##     ## create visitor object
+    ##     require 'psych'
+    ##     require 'psych/visitors/custom_class'
+    ##     classmap = {
+    ##       "teams"   => Team,
+    ##       "members" => Member,
+    ##     }
+    ##     visitor = Psych::Visitors::CustomClassVisitor.create(classmap)
+    ##     ## parse YAML document with custom classes
+    ##     input = <<-'END'
+    ##     teams:
+    ##       - name: SOS Brigade
+    ##         members:
+    ##           - {name: Haruhi, gender: F}
+    ##           - {name: Kyon,   gender: M}
+    ##           - {name: Mikuru, gender: F}
+    ##           - {name: Itsuki, gender: M}
+    ##           - {name: Yuki,   gender: F}
+    ##     END
+    ##     tree = Psych.parse(input)
+    ##     ydoc = visitor.accept(tree)
+    ##     p ydoc['teams'][0].class                #=> Struct::Team
+    ##     p ydoc['teams'][0]['members'][0].class  #=> Struct::Member
+    ##     team = ydoc['teams'][0]
+    ##     p team.name                #=> "SOS Brigade"
+    ##     p team.members[0].name     #=> "Haruhi"
+    ##     p team.members[0].gender   #=> "F"
+    ##
+    class CustomClassVisitor < ToRuby
+
+      def self.create(classmap={})
+        visitor = super()
+        visitor.instance_variable_set('@classmap', classmap)
+        visitor
+      end
+
+      attr_reader :classmap   # key: string, value: class object
+
+      def initialize(*args)
+        super
+        @key_path = []     # ex: [] -> ['tables'] -> ['tables', 'columns']
+      end
+
+      def accept_key(k)    # push keys
+        key = super k
+        @key_path << key
+        key
+      end
+
+      def accept_value(v)  # pop keys
+        value = super v
+        @key_path.pop()
+        value
+      end
+
+      def empty_mapping(o)  # generate custom object (or Hash object)
+        klass = @classmap[@key_path.last]
+        klass ? klass.new : super
+      end
+
+      def merge_mapping(hash, val)   # for '<<' (merge)
+        val.each {|k, v| hash[k] = v }
+      end
+
+    end
+
+  end
+end
-- 
2.9.3 (Apple Git-75)