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.
# File lib/active_support/ordered_hash.rb, line 73 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
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/active_support/ordered_hash.rb, line 68 def initialize(*args, &block) super @keys = [] end
# File lib/active_support/ordered_hash.rb, line 103 def []=(key, value) @keys << key unless has_key?(key) super end
# File lib/active_support/ordered_hash.rb, line 174 def clear super @keys.clear self end
# File lib/active_support/ordered_hash.rb, line 108 def delete(key) if has_key? key index = @keys.index(key) @keys.delete_at index end super end
# File lib/active_support/ordered_hash.rb, line 116 def delete_if super sync_keys! self end
# File lib/active_support/ordered_hash.rb, line 160 def each return to_enum(:each) unless block_given? @keys.each {|key| yield [key, self[key]]} self end
# File lib/active_support/ordered_hash.rb, line 148 def each_key return to_enum(:each_key) unless block_given? @keys.each { |key| yield key } self end
# File lib/active_support/ordered_hash.rb, line 166 def each_pair return to_enum(:each_pair) unless block_given? @keys.each {|key| yield key, self[key]} self end
# File lib/active_support/ordered_hash.rb, line 154 def each_value return to_enum(:each_value) unless block_given? @keys.each { |key| yield self[key]} self end
# File lib/active_support/ordered_hash.rb, line 28 def encode_with(coder) coder.represent_seq '!omap', map { |k,v| { k => v } } end
Returns true to make sure that this hash is extractable via
Array#extract_options!
# File lib/active_support/ordered_hash.rb, line 51 def extractable_options? true end
# File lib/active_support/ordered_hash.rb, line 97 def initialize_copy(other) super # make a deep copy of keys @keys = other.keys end
# File lib/active_support/ordered_hash.rb, line 212 def inspect "#<OrderedHash #{super}>" end
# File lib/active_support/ordered_hash.rb, line 208 def invert OrderedHash[self.to_a.map!{|key_value_pair| key_value_pair.reverse}] end
# File lib/active_support/ordered_hash.rb, line 132 def keys @keys.dup end
# File lib/active_support/ordered_hash.rb, line 197 def merge(other_hash, &block) dup.merge!(other_hash, &block) end
# File lib/active_support/ordered_hash.rb, line 186 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
# File lib/active_support/ordered_hash.rb, line 46 def nested_under_indifferent_access self end
# File lib/active_support/ordered_hash.rb, line 128 def reject(&block) dup.reject!(&block) end
# File lib/active_support/ordered_hash.rb, line 122 def reject! super sync_keys! self end
When replacing with another hash, the initial order of our keys must come from the other hash -ordered or not.
# File lib/active_support/ordered_hash.rb, line 202 def replace(other) super @keys = other.keys self end
# File lib/active_support/ordered_hash.rb, line 180 def shift k = @keys.first v = delete(k) [k, v] end
# File lib/active_support/ordered_hash.rb, line 217 def sync_keys! @keys.delete_if {|k| !has_key?(k)} end
# File lib/active_support/ordered_hash.rb, line 144 def to_a @keys.map { |key| [ key, self[key] ] } end
# File lib/active_support/ordered_hash.rb, line 140 def to_hash self end
# File lib/active_support/ordered_hash.rb, line 32 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
# File lib/active_support/ordered_hash.rb, line 24 def to_yaml_type "!tag:yaml.org,2002:omap" end
# File lib/active_support/ordered_hash.rb, line 136 def values @keys.collect { |key| self[key] } end