Ruby:哈希中的自引用

Question

是否可以在同一哈希中的另一个元素中引用哈希中的一个元素？

# Pseudo code
foo = { :world => "World", :hello => "Hello #{foo[:world]}" }
foo[:hello] # => "Hello World"

Answer 1

间接地也许......

foo = { :world => 'World', :hello => lambda { "Hello #{foo[:world]}" }}

puts foo[:hello].call

Answer 2

如果您想使某些键的值依赖于其他键:

foo = Hash.new{|h, k|
   case k
   when :hello; "Hello #{h[:world]}"
   when :bye; "Bye #{h[:world]}"
   end
}
foo[:world] = 'World'
foo[:hello] # => 'Hello World'
foo[:bye] # => 'Bye World'
foo[:world] = 'Heaven'
foo[:hello] # => 'Hello Heaven'
foo[:bye] # => 'Bye Heaven'