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Are you tired of calling .freeze on your data structures (or your colleagues forgetting to do so)?
Do you wish Ruby had a literal for creating immutable arrays?

Then persistent-💎 aka persistent diamond is for you!

Persistent-💎 gives you a very tidy way of creating immutable…​

  • Arrays:

    my_array = a💎[1, 2, 3]

  • Hashes:

    my_hash = h💎[key1: 'foo', key2: 'bar']

  • Sets:

    my_set = s💎[:sephiroth, :kills, :aeris]

…​and it behaves as you expect it to:

  • You can compare immutable data structures with regular Ruby instances

    a💎[1, 2] == [1, 2] && h💎[key1: 'foo'] == {key1: 'foo'} && s💎[:hello] == Set.new([:hello])
# => true

  • You can compare immutable hashes with </<=/>=/> and with regular Ruby hashes:

    h💎[a: 1] < h💎[a: 1, b: 2] && {a: 1, b: 2} < h💎[a: 1, b: 2, c: 3]
# => true

  • You can compare immutable sets with </<=/>=/> and with regular Ruby sets:

    s💎[1] < s💎[1, 2] && Set.new([1, 2]) < s💎[1, 2, 3]
# => true

  • You can splat (*) immutable arrays:

    def sum(a, b, c)
  a + b + c
end

sum(*a💎[1, 2, 39])
# => 42

sum(1, *a💎[2, 39])
# => 42

  • You can double-splat (**) immmutable hashes:

    def hello(name:, age:)
  "Hello there #{name}, you are #{age} years old!"
end

hello(h💎[name: 'User', age: '50'])
# => "Hello there User, you are 50 years old!"

hello(name: 'Another User', **h💎[age: '50'])
# => "Hello there Another User, you are 50 years old!"

Beyond being immutable, these data structures are thread-safe, and can be efficiently copied: when you "update" them, a new copy gets created that shares most of its structure with the original. Thus, creating new instances from existing structures is both memory-efficient and quite fast!

It also (optionally!) interoperates with the concurrent-ruby gem, for when you need that extra Oomph (or just thread-safe mutability). See below for more details.

Underneath the covers, persistent-💎 mostly builds atop the awesome hamster gem. Big thanks to its equally-awesome authors!

Persistent-💎 is fully supported and tested on Ruby versions 1.9.3 to 2.5, and JRuby 1.7 to to 9.1. If we don’t support your Ruby, it’s probably a Python binary. Keep calm and 💎 away!

Contents

Installation

Add this line to your application’s gems.rb or Gemfile:

gem 'persistent-dmnd'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install persistent-dmnd

This gem is versioned according to Semantic Versioning.

Usage

To use persistent-💎, first load it:

require 'persistent-💎'
# note: you can also use require 'persistent-dmnd'

Persistent-💎 can be added as a module to individual classes (or even to other modules!):

class FooController
  include Persistent💎
  # note: you can also use include PersistentDmnd

  ARGUMENTS = a💎[:name, :address, :likes_icecream] # Usable inside this class...

  def stuff
    a💎[:stuff, :more_stuff] # ...and its methods
  end
end

Or you can add it to your whole application by just doing

require 'persistent_dmnd/everywhere'

a💎[:freeeeeeedooooom] # usable everyhere in your application

As you may have noticed, everywhere there is an 💎, you can replace it with dmnd, e.g. PersistentDmnd instead of Persistent💎 for the gem module and for aDmnd[] instead of a💎[] to create an array.

Creating new persistent structures

Array

Use a💎[] (or aDmnd[]) to create a new array:

empty_array = a💎[]
# => Persistent💎::Array[]

my_array = a💎[:hello, :world]
# => Persistent💎::Array[:hello, :world]

Hash

Use h💎[] (or hDmnd[]) to create a new hash:

empty_hash = h💎[]
# => Persistent💎::Hash[]

my_hash = h💎['hello' => 'world']
# => Persistent💎::Hash["hello" => "world"]

Set

Use s💎[] (or sDmnd[]) to create a new set:

empty_set = s💎[]
# => Persistent💎::Set[]

2.4.2 :028 > my_set = s💎[:hello, :world]
# => Persistent💎::Set[:hello, :world]

Converting from existing structures

You can use 💎ify[] (or dmndify[]) to convert any received argument to a persistent structure (without modifying the original). It is great for getting a protected copy of your input, that you can now store, operate on and share among threads without concern.

It works for all the persistent structures above:

my_array = a💎[:hello, :world]
💎ify[my_array]
# => Persistent💎::Array[:hello, :world]

my_hash = h💎['hello' => 'world']
💎ify[my_hash]
# => Persistent💎::Hash["hello" => "world"]

my_set = s💎[:hello, :world]
💎ify[my_set]
# => Persistent💎::Set[:hello, :world]

It works for regular Ruby arrays (and any object that implements to_ary()):

my_array = [:regular, :ruby, :array]
💎ify[my_array]
# => Persistent💎::Array[:regular, :ruby, :array] # Not regular any more! :)

It works for regular Ruby hashes (and any object that implements to_hash()):

my_hash = {regular: :ruby, hash: nil}
💎ify[my_hash]
# => Persistent💎::Hash[:hash => nil, :regular => :ruby]

It works for regular Ruby sets (and any object that implements to_set()):

my_set = Set.new([:regular, :ruby, :set])
💎ify[my_set]
=> Persistent💎::Set[:regular, :ruby, :set]

And it works for hamster gem (Hamster::Vector, Hamster::Hash, Hamster::Set) and concurrent-ruby gem (Concurrent::Array, Concurrent::Tuple, Concurrent::Hash, Concurrent::Map) data structures:

my_vector = Hamster::Vector[1, 2, 3]
💎ify[my_vector]
# => Persistent💎::Array[1, 2, 3]

my_array = Concurrent::Array[1, 2, 3]
💎ify[my_array]
# => Persistent💎::Array[1, 2, 3]

my_tuple = Concurrent::Tuple.new(1)
my_tuple.set(0, :hello)
💎ify[my_tuple]
# => Persistent💎::Array[:hello]

my_hash = Hamster::Hash[hello: :world]
💎ify[my_hash]
# => Persistent💎::Hash[:hello => :world]

my_hash = Concurrent::Hash[hello: :world]
💎ify[my_hash]
# => Persistent💎::Hash[:hello => :world]

my_map = Concurrent::Map.new
my_map[:hello] = :world
💎ify[my_map]
# => Persistent💎::Hash[:hello => :world]

my_set = Hamster::Set[:hello, :world]
💎ify[my_set]
# => Persistent💎::Set[:hello, :world]

And you can even implement it on your own classes:

class MyList
  include Persistent💎

  def initialize(item1, item2, item3)
    @item1 = item1
    @item2 = item2
    @item3 = item3
  end

  def to_💎 # can also be #to_dmnd
    a💎[@item1, @item2, @item3]
  end
end

my_list = MyList.new(:hello, :there, :readers)
💎ify[my_list]
# => Persistent💎::Array[:hello, :there, :readers]

Converting to regular Ruby structures

The usual to_a()/to_h()/to_set() can be used to convert persistent data structures back to their regular Ruby counterparts:

a💎[1, 2].to_a
# => [1, 2]

h💎[hello: :world].to_h
# => {:hello=>:world}

s💎[1, 2].to_set
# => #<Set: {1, 2}>

Converting between persistent structures

All three persistent structures implement to_a💎() (or to_aDmnd()), to_h💎() (or to_hDmnd()) and to_s💎() (or to_sDmnd()) as persistent counterparts for the usual Ruby to_a(), to_h() and to_s():

a💎[1, 2].to_a💎
# => Persistent💎::Array[1, 2]

a💎[1, 2].to_s💎
# => Persistent💎::Set[1, 2]

a💎[['hello', 'world']].to_h💎
# => Persistent💎::Hash["hello" => "world"]


h💎['hello' => 'world'].to_h💎
# => Persistent💎::Hash["hello" => "world"]

h💎['hello' => 'world'].to_a💎
# => Persistent💎::Array[Persistent💎::Array["hello", "world"]]

h💎['hello' => 'world'].to_s💎
# => Persistent💎::Set[Persistent💎::Array["hello", "world"]]


s💎[1, 2].to_s💎
# => Persistent💎::Set[1, 2]

s💎[1, 2].to_a💎
# => Persistent💎::Array[1, 2]

s💎[['hello', 'world']].to_h💎
# => Persistent💎::Hash["hello" => "world"]

Concurrent Ruby interoperability

When you need to go from thread-safe immutable data structures to thread-safe mutable data structures you can use Persistent-💎's optional interoperability with the concurrent-ruby gem.

You’ll need to install concurrent-ruby first, see https://github.com/ruby-concurrency/concurrent-ruby#installation for instructions.

After that, you’ll be able to:

Array

Use to_concurrent() (or to_concurrent_array()) to convert your array into a Concurrent::Array:

my_array = a💎[:hello, :world]
my_concurrent_array = my_array.to_concurrent

Use to_concurrent_tuple() to convert your array into a Concurrent::Tuple:

my_array = a💎[:hello, :world]
my_concurrent_tuple = my_array.to_concurrent_tuple
# => #<Concurrent::Tuple @size=2, @tuple=[<#Concurrent::AtomicReference value:hello>, <#Concurrent::AtomicReference value:world>]>

Hash

Use to_concurrent() (or to_concurrent_hash()) to convert your hash into a Concurrent::Hash:

my_hash = h💎[hello: :world]
my_concurrent_hash = my_hash.to_concurrent

Use to_concurrent_map() to convert your hash into a Concurrent::Map:

my_hash = h💎[hello: :world]
my_concurrent_map = my_hash.to_concurrent_map
# => #<Concurrent::Map:0x0055ad9b283ea0 entries=1 default_proc=nil>

API documentation for the persistent structures

Because the persistent structures are provided by the awesome hamster gem, you can refer back to Hamster’s API docs for details on the operations provided by each data structure.

Array

Built on top of Hamster::Vector

Hash

Built on top of Hamster::Hash

Set

Built on top of Hamster::Set

AAARGH YOU FIEND WHY IS THERE AN EMOJI ON MY CODEBASE?

Every printable ascii character is already in use by Ruby, but I didn’t want persistent data structures to clutter my source code. I also did not want to use cryptic single, two-letter or three-letter acronyms. Ruby is supposed to be beautifully readable!

Thus, I kept my Ruby beautiful. With two very clear characters you can create an immutable data structure. No more awkward typing of namespaces. No more .freeze everywhere. No-one will ever mistake the use of 💎 for another operation.

Now you can avoid having 💎 on your codebase altogether: just use dmnd, as suggested above.

If you’re having a hard time typing the emoji, I recommend just adding a quick snippet to your editor or a quick command to search-and-replace aDmnd/hDmnd/sDmnd/dmndify for a💎/h💎/s💎/💎ify. That way you get best of both worlds: easy to type, and easy to read!

Usage on Ruby 1.9

Because of our usage of emojis for method names, you’ll need to add

# encoding: UTF-8

as the first (or second) line of any file that uses Persistent-💎. As an alternative, you can also use the dmnd syntax.

This setting is the default from Ruby 2.0 on, so users of later versions do not need to worry about this small detail.

Development

After checking out the repo, run bundle install to install dependencies. Then, run rake spec to run the tests.

To open a console with the gem loaded, run bundle console.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/ivoanjo/persistent-dmnd.

This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

Maintained with 💎❤️ by Ivo Anjo.

Thanks

Thanks to these amazing people for their contributions!

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the Persistent-💎 project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.

Interesting links

Interested in immutable/persistent data structures? Here are some interesting resources for your exploration: