Ruby/Hash/Hash.new
Материал из Wiki.crossplatform.ru
Версия от 17:57, 13 сентября 2010; ViGOur (Обсуждение | вклад)
access any key in a hash that has a default value
if the key or value doesn"t exist, accessing the hash will return the default value: months = Hash.new( "month" ) months[0] # or: months[72] # or: months[234]
Creating Hashes
# You can create an empty hash with the new class method. months = Hash.new
Hash.new with block logic
p h = Hash.new { |hash, key| (key.respond_to? :to_str) ? "nope" : nil } p h[1] # => nil p h["do"] # => "nope"
Hash with =>
myHash = Hash[ :name => "Jack", :partner => "Jane", :employee => "Joe" =>:location,"London", :year => 1843 ]
Test how big it is with length or size
months = Hash.new months.length months.size # => 0
This lazily initialized hash maps integers to their factorials
fact = Hash.new {|h,k| h[k] = if k > 1: k*h[k-1] else 1 end } p fact # {}: it starts off empty p fact[4] # 24: 4! is 24 p fact # {1=>1, 2=>2, 3=>6, 4=>24}: the hash now has entries
use new to create a hash with a default value which is otherwise just nil
months = Hash.new( "month" ) # or like this: months = Hash.new "month"
You can test to see if a hash is empty with empty?
months = Hash.new months.empty? # => true
