property_hash.rb in hashery-1.5.0

- old
+ new
@@ -1,96 +1,192 @@
-require 'hashery/propertyhash'
+# A PropertyHash is the same as a regular Hash except it strictly limits the
+# allowed keys.
+#
+# There are two ways to use it.
+#
+# 1) As an object in itself.
+#
+#   h = PropertyHash.new(:a=>1, :b=>2)
+#   h[:a]        #=> 1
+#   h[:a] = 3
+#   h[:a]        #=> 3
+#
+# But if we try to set key that was not fixed, then we will get an error.
+#
+#   h[:x] = 5    #=> ArgumentError
+# 
+# 2) As a superclass.
+#
+#   class MyPropertyHash < PropertyHash
+#     property :a, :default => 1
+#     property :b, :default => 2
+#   end
+#
+#   h = MyPropertyHash.new
+#   h[:a]        #=> 1
+#   h[:a] = 3
+#   h[:a]        #=> 3
+#
+# Again, if we try to set key that was not fixed, then we will get an error.
+#
+#   h[:x] = 5    #=> ArgumentError
+#
+class PropertyHash < Hash
+
+  #
+  def self.properties
+    @properties ||= (
+      parent = ancestors[1]
+      if parent.respond_to?(:properties)
+        parent.properties
+      else
+        {}
+      end
+    )
+  end
+
+  #
+  def self.property(key, opts={})
+    properties[key] = opts[:default]
+  end
+
+  #
+  def initialize(properties={})
+    super()
+    fixed = self.class.properties.merge(properties)
+    replace(fixed)
+  end
+
+  #
+  def []=(k,v)
+    assert_key!(k)
+    super(k,v)
+  end
+
+  #
+  def update(h)
+    h.keys.each{ |k| assert_key!(k) }
+    super(h)
+  end
+
+  #
+  def merge!(h)
+    h.keys.each{ |k| assert_key!(k) }
+    super(h)
+  end
+
+  #
+  def <<(a)
+    k,v = *a
+    self[k] = v
+  end
+
+  # Add a new acceptable key.
+  # TODO: Should this be supported?
+  def accept_key!(k,v=nil)
+    self[k] = v
+  end
+
+  private
+
+  def assert_key!(key)
+    unless key?(key)
+      raise ArgumentError, "The key '#{key}' is not defined for this FixedHash."
+    end
+  end
+
+end