Semintelligent

Freezing Ruby Data Structures Recursively · 15 September 2008, 10:18

Flavorrific published a monkey patch that extends Object with a deep freeze method that freezes child arrays and hashes of a data structure so that they aren’t accidentally changed (for example, configuration data from YAML).

I have extended his work in the following ways:


class Object

# Define a deep_freeze method in Object (based on code posted by flavorrific # http://flavoriffic.blogspot.com/2008/08/freezing-deep-ruby-data-structures.html) # that will call freeze on the top-level object instance the method is # called on in as well as any child object instances contained in the # parent. This patch will also raise an IndexError if keys from # ‘deeply frozen’ Hashes or Arrays are accessed that do not exist.

def deep_freeze

# String doesn’t support each if (self.class != String) && (self.respond_to? :each) each { |v| v.deep_freeze if v.respond_to?(:deep_freeze) } end # Deep freeze instance variable values if self.kind_of? Object self.instance_variables.each { |v| iv = self.instance_variable_get(v) iv.deep_freeze self.instance_variable_set(v, iv) } end if self.kind_of? Hash instance_eval(<<EOF) def default(key) raise IndexError, “Frozen hash: key ‘\#{key}’ does not exist!” end EOF end # Prevent user from accessing array elements that do not exist. if self.kind_of? Array instance_eval(<<EOF) def at(index) self.fetch(index) end def [](arg1, arg2 = nil) results = Array.new if ! arg2.nil? # Start index and end index given arg1.upto(arg1 + arg2) { |index| results << self.fetch(index) } else if arg1.kind_of? Range # Range passed in arg1.each { |index| results << self.fetch(index) } else results << self.fetch(arg1) end end results end EOF end # Freeze the current structure freeze end

end

— Max Schubert

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