这并不完全是一行程序，但是它将所有字符串键转换为符号，包括嵌套的符号:

def recursive_symbolize_keys(my_hash)
  case my_hash
  when Hash
    Hash[
      my_hash.map do |key, value|
        [ key.respond_to?(:to_sym) ? key.to_sym : key, recursive_symbolize_keys(value) ]
      end
    ]
  when Enumerable
    my_hash.map { |value| recursive_symbolize_keys(value) }
  else
    my_hash
  end
end

这个怎么样:

my_hash = HashWithIndifferentAccess.new(YAML.load_file('yml'))

# my_hash['key'] => "val"
# my_hash[:key]  => "val"

这并不完全是一行程序，但是它将所有字符串键转换为符号，包括嵌套的符号:

def recursive_symbolize_keys(my_hash)
  case my_hash
  when Hash
    Hash[
      my_hash.map do |key, value|
        [ key.respond_to?(:to_sym) ? key.to_sym : key, recursive_symbolize_keys(value) ]
      end
    ]
  when Enumerable
    my_hash.map { |value| recursive_symbolize_keys(value) }
  else
    my_hash
  end
end

http://api.rubyonrails.org/classes/Hash.html#method-i-symbolize_keys

hash = { 'name' => 'Rob', 'age' => '28' }
hash.symbolize_keys
# => { name: "Rob", age: "28" }

对于Ruby中YAML的特定情况，如果键以':'开头，它们将被自动作为符号存储。

require 'yaml'
require 'pp'
yaml_str = "
connections:
  - host: host1.example.com
    port: 10000
  - host: host2.example.com
    port: 20000
"
yaml_sym = "
:connections:
  - :host: host1.example.com
    :port: 10000
  - :host: host2.example.com
    :port: 20000
"
pp yaml_str = YAML.load(yaml_str)
puts yaml_str.keys.first.class
pp yaml_sym = YAML.load(yaml_sym)
puts yaml_sym.keys.first.class

输出:

#  /opt/ruby-1.8.6-p287/bin/ruby ~/test.rb
{"connections"=>
  [{"port"=>10000, "host"=>"host1.example.com"},
   {"port"=>20000, "host"=>"host2.example.com"}]}
String
{:connections=>
  [{:port=>10000, :host=>"host1.example.com"},
   {:port=>20000, :host=>"host2.example.com"}]}
Symbol

ruby-1.9.2-p180 :001 > h = {'aaa' => 1, 'bbb' => 2}
 => {"aaa"=>1, "bbb"=>2} 
ruby-1.9.2-p180 :002 > Hash[h.map{|a| [a.first.to_sym, a.last]}]
 => {:aaa=>1, :bbb=>2}