class OrderedHash

The order of iteration over hashes in Ruby 1.8 is undefined. For example, you do not know the order in which keys will return keys, or each yield pairs. ActiveSupport::OrderedHash implements a hash that preserves insertion order, as in Ruby 1.9:

oh = ActiveSupport::OrderedHash.new
oh[:a] = 1
oh[:b] = 2
oh.keys # => [:a, :b], this order is guaranteed

ActiveSupport::OrderedHash is namespaced to prevent conflicts with other implementations.

Public Class Methods

[](*args) click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 74
def self.[](*args)
  ordered_hash = new

  if (args.length == 1 && args.first.is_a?(Array))
    args.first.each do |key_value_pair|
      next unless (key_value_pair.is_a?(Array))
      ordered_hash[key_value_pair[0]] = key_value_pair[1]
    end

    return ordered_hash
  end

  unless (args.size % 2 == 0)
    raise ArgumentError.new("odd number of arguments for Hash")
  end

  args.each_with_index do |val, ind|
    next if (ind % 2 != 0)
    ordered_hash[val] = args[ind + 1]
  end

  ordered_hash
end
new(*args, &block) click to toggle source

In MRI the Hash class is core and written in C. In particular, methods are programmed with explicit C function calls and polymorphism is not honored.

For example, []= is crucial in this implementation to maintain the @keys array but hash.c invokes rb_hash_aset() originally. This prevents method reuse through inheritance and forces us to reimplement stuff.

For instance, we cannot use the inherited merge! because albeit the algorithm itself would work, our []= is not being called at all by the C code.

# File lib/deltacloud/core_ext/ordered_hash.rb, line 69
def initialize(*args, &block)
  super
  @keys = []
end

Public Instance Methods

[]=(key, value) click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 104
def []=(key, value)
  @keys << key unless has_key?(key)
  super
end
clear() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 175
def clear
  super
  @keys.clear
  self
end
delete(key) click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 109
def delete(key)
  if has_key? key
    index = @keys.index(key)
    @keys.delete_at index
  end
  super
end
delete_if() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 117
def delete_if
  super
  sync_keys!
  self
end
each() { |key, self| ... } click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 161
def each
  return to_enum(:each) unless block_given?
  @keys.each {|key| yield [key, self[key]]}
  self
end
each_key() { |key| ... } click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 149
def each_key
  return to_enum(:each_key) unless block_given?
  @keys.each { |key| yield key }
  self
end
each_pair() { |key, self| ... } click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 167
def each_pair
  return to_enum(:each_pair) unless block_given?
  @keys.each {|key| yield key, self[key]}
  self
end
each_value() { |self| ... } click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 155
def each_value
  return to_enum(:each_value) unless block_given?
  @keys.each { |key| yield self[key]}
  self
end
encode_with(coder) click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 29
def encode_with(coder)
  coder.represent_seq '!omap', map { |k,v| { k => v } }
end
extractable_options?() click to toggle source

Returns true to make sure that this hash is extractable via Array#extract_options!

# File lib/deltacloud/core_ext/ordered_hash.rb, line 52
def extractable_options?
  true
end
initialize_copy(other) click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 98
def initialize_copy(other)
  super
  # make a deep copy of keys
  @keys = other.keys
end
inspect() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 213
def inspect
  "#<OrderedHash #{super}>"
end
invert() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 209
def invert
  OrderedHash[self.to_a.map!{|key_value_pair| key_value_pair.reverse}]
end
keys() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 133
def keys
  @keys.dup
end
merge(other_hash, &block) click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 198
def merge(other_hash, &block)
  dup.merge!(other_hash, &block)
end
merge!(other_hash) { |k, self, v| ... } click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 187
def merge!(other_hash)
  if block_given?
    other_hash.each { |k, v| self[k] = key?(k) ? yield(k, self[k], v) : v }
  else
    other_hash.each { |k, v| self[k] = v }
  end
  self
end
nested_under_indifferent_access() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 47
def nested_under_indifferent_access
  self
end
reject(&block) click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 129
def reject(&block)
  dup.reject!(&block)
end
reject!() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 123
def reject!
  super
  sync_keys!
  self
end
replace(other) click to toggle source

When replacing with another hash, the initial order of our keys must come from the other hash -ordered or not.

# File lib/deltacloud/core_ext/ordered_hash.rb, line 203
def replace(other)
  super
  @keys = other.keys
  self
end
shift() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 181
def shift
  k = @keys.first
  v = delete(k)
  [k, v]
end
sync_keys!() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 218
def sync_keys!
  @keys.delete_if {|k| !has_key?(k)}
end
to_a() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 145
def to_a
  @keys.map { |key| [ key, self[key] ] }
end
to_hash() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 141
def to_hash
  self
end
to_yaml(opts = {}) click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 33
def to_yaml(opts = {})
  if YAML.const_defined?(:ENGINE) && !YAML::ENGINE.syck?
    return super
  end

  YAML.quick_emit(self, opts) do |out|
    out.seq(taguri) do |seq|
      each do |k, v|
        seq.add(k => v)
      end
    end
  end
end
to_yaml_type() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 25
def to_yaml_type
  "!tag:yaml.org,2002:omap"
end
values() click to toggle source
# File lib/deltacloud/core_ext/ordered_hash.rb, line 137
def values
  @keys.collect { |key| self[key] }
end