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Immutable collections in Ruby with Hamster

· [neiro]

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:

If you want to make Ruby hash immutable, you can use freeze it:

1immutable = { foo: 'bar' } immutable.freeze
2
3immutable[: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.

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:

1gem i hamster
2require 'hamster'

or only certain types:

1require 'hamster/hash'
2require 'hamster/vector'
3require 'hamster/set'
4require 'hamster/sorted_set'
5require 'hamster/list'
6require 'hamster/deque'

Hash

 1# Create new Hamster Hash
 2parrot = Hamster::Hash[type: 'bird', class: 'parrot', color: 'yellow']
 3
 4parrot.get(:color) # yellow
 5parrot[:type] # bird
 6
 7# You can not change hash because of immutability
 8parrot[:subclass] = 'budgie' # NoMethodError: undefined method `[]='
 9# But you can create a new
10
11budgie = parrot.put :subclass, 'budgie'
12budgie == parrot # false
13budgie[:subclass] # budgie
14parrot[:subclass] # nil
15
16budgie.to_hash.class # Plain Ruby Hash

List

1list = Hamster::List[0, 1, 2] list.tail # Hamster::List[1, 2]
2list.head # 0

Set

 1# Hamster's set is an unordered collection with no duplicates
 2colors = Hamster::Set[:green, :white]
 3colors.include?(:green) # true
 4
 5palette = colors.add :yellow # Hamster::Set[:green, :yellow, :white]
 6colors.include?(:yellow) # false palette.superset?(colors) # true
 7palette.intersection(colors) # Hamster::Set[:green, :white]
 8palette.difference(colors).first # :yellow
 9
10palette.to_a # Plain Ruby array: [:green, :white, :yellow]

Vector

 1 # Vector is an integer-indexed immutable array
 2vector = Hamster::Vector[0, 1, 2]
 3vector[2] # 2
 4vector[-1] # 2
 5vector[-4] # nil
 6vector[1,2] # Hamster::Vector[1, 2]
 7vector[0..2] # Hamster::Vector[0, 1, 2]
 8
 9binary_vector = vector.delete_at 0 # Hamster::Vector[1, 2]
10vector.size # 3
11binary_vector.size # 2
12vector == binary_vector # false
13
14(binary_vector + vector).sort.uniq # Hamster::Vector[0, 1, 2]
15(binary_vector + vector).sort.uniq == vector # true

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.

#ruby #functional #immutable