Immutable collections in Ruby with Hamster
Ruby has much in common with functional programming languages. For example, Ruby supports high-order functions, lambdas, currying and recursion, but not the immutability - Ruby’s types and data structures are mutable and can be changed at any time.
Why immutability is important? The’re many arguments for that:
- reliability
- thread-safety
- simpler debugging
- purity - immutable data allows you to write side-effects free code
If you want to make Ruby hash immutable, you can use freeze it:
immutable = { foo: 'bar' } immutable.freeze
immutable[:foo] = 'tball'# RuntimeError: can't modify frozen Hash
But if you want to use already immutable collections, sets and other data structures, you can try Hamster library.
1 Hamster
Hamster provides efficient, immutable and thread-safe collection classes for Ruby, such as Hash, Vector, Set, SortedSet and List. Hamster collections offers Ruby`s Hash, Array, Enumberable compatibility where it possible. You can require all of Hamster collection classes:
gem i hamster require 'hamster'
or only certain types:
require 'hamster/hash' require 'hamster/vector' require 'hamster/set' require 'hamster/sorted_set' require 'hamster/list' require 'hamster/deque'
2 Hash
# Create new Hamster Hash parrot = Hamster::Hash[type: 'bird', class: 'parrot', color: 'yellow'] parrot.get(:color) # yellow parrot[:type] # bird # You can not change hash because of immutability parrot[:subclass] = 'budgie' # NoMethodError: undefined method `[]=' # But you can create a new budgie = parrot.put :subclass, 'budgie' budgie == parrot # false budgie[:subclass] # budgie parrot[:subclass] # nil budgie.to_hash.class # Plain Ruby Hash
3 List
list = Hamster::List[0, 1, 2] list.tail # Hamster::List[1, 2] list.head # 0
4 Set
# Hamster's set is an unordered collection with no duplicates colors = Hamster::Set[:green, :white] colors.include?(:green) # true palette = colors.add :yellow # Hamster::Set[:green, :yellow, :white] colors.include?(:yellow) # false palette.superset?(colors) # true palette.intersection(colors) # Hamster::Set[:green, :white] palette.difference(colors).first # :yellow palette.to_a # Plain Ruby array: [:green, :white, :yellow]
5 Vector
# Vector is an integer-indexed immutable array vector = Hamster::Vector[0, 1, 2] vector[2] # 2 vector[-1] # 2 vector[-4] # nil vector[1,2] # Hamster::Vector[1, 2] vector[0..2] # Hamster::Vector[0, 1, 2] binary_vector = vector.delete_at 0 # Hamster::Vector[1, 2] vector.size # 3 binary_vector.size # 2 vector == binary_vector # false (binary_vector + vector).sort.uniq # Hamster::Vector[0, 1, 2] (binary_vector + vector).sort.uniq == vector # true
6 Conclusion
If you want to use immutable data structures in Ruby to write more reliable, efficient and at the same time thread-safe code, you can take a look at Hamster. You can find more in Hamster’s API documentation.