Wholeable

Wholeable allows you to turn your object into a whole value object by ensuring object equality is determined by the values of the object instead of by identity. Whole value objects — or value objects in general — have the following traits as noted via Wikipedia:

Equality is determined by the values that make up an object and not by identity (i.e. memory address) which is the default behavior for all Ruby objects except for Data and Structs.
Identity remains unique since two objects can have the same values but different identity. This means BasicObject#equal? is never overwritten — which is strongly discouraged — as per BasicObject documentation.
Value objects should be immutable (i.e. frozen) by default. This implementation enforces a strict adherence to immutability in order to ensure value objects remain equal and discourage mutation.

Table of Contents

Features
Requirements
Setup
Usage
- Initialization
- Mutability
- Inheritance
Caveats
Performance
Development
Tests
License
Security
Code of Conduct
Contributions
Developer Certificate of Origin
Versions
Community
Credits

Features

Ensures equality (i.e. #== and #eql?) is determined by attribute values and not object identity (i.e. #equal?).
Allows you to compare two objects of same or different types and see their differences.
Provides pattern matching.
Provides inheritance so you can subclass and add attributes or provide additional behavior.
Automatically defines public attribute readers (i.e. .attr_reader) if immutable (default) or public attribute readers and writers (i.e. .attr_accessor) if mutable.
Ensures object inspection (i.e. #inspect) shows all registered attributes.
Ensures object is frozen upon initialization by default.

Requirements

Ruby.

Setup

To install with security, run:

# 💡 Skip this line if you already have the public certificate installed.
gem cert --add <(curl --compressed --location https://alchemists.io/gems.pem)
gem install wholeable --trust-policy HighSecurity

To install without security, run:

gem install wholeable

You can also add the gem directly to your project:

bundle add wholeable

Once the gem is installed, you only need to require it:

require "wholeable"

Usage

To use, include Wholeable along with a list of attributes that make up your whole value object:

class Person
  include Wholeable[:name, :email]

  def initialize name:, email:
    @name = name
    @email = email
  end
end

jill = Person[name: "Jill Smith", email: "jill@example.com"]
jill_two = Person[name: "Jill Smith", email: "jill@example.com"]
jack = Person[name: "Jack Smith", email: "jack@example.com"]

Person.members         # [:name, :email]
jill.members           # [:name, :email]

jill.name              # "Jill Smith"
jill.email             # "jill@example.com"

jill.frozen?           # true
jill_two.frozen?       # true
jack.frozen?           # true

jill.inspect           # "#<Person @name=\"Jill Smith\", @email=\"jill@example.com\">"
jill_two.inspect       # "#<Person @name=\"Jill Smith\", @email=\"jill@example.com\">"
jack.inspect           # "#<Person @name=\"Jack Smith\", @email=\"jack@example.com\">"

jill == jill           # true
jill == jill_two       # true
jill == jack           # false

jill.diff(jill)        # {}
jill.diff(jack)        # {
                       #   name: ["Jill Smith", "Jack Smith"],
                       #   email: ["jill@example.com", "jack@example.com"]
                       # }
jill.diff(Object.new)  # {:name=>["Jill Smith", nil], :email=>["jill@example.com", nil]}

jill.eql? jill         # true
jill.eql? jill_two     # true
jill.eql? jack         # false

jill.equal? jill       # true
jill.equal? jill_two   # false
jill.equal? jack       # false

jill.hash              # 3650965837788801745
jill_two.hash          # 3650965837788801745
jack.hash              # 4460658980509842640

jill.to_a              # ["Jill Smith", "jill@example.com"]
jack.to_a              # ["Jack Smith", "jack@example.com"]

jill.to_h              # {:name=>"Jill Smith", :email=>"jill@example.com"}
jack.to_h              # {:name=>"Jack Smith", :email=>"jack@example.com"}

jill.to_s              # "#<Person @name=\"Jill Smith\", @email=\"jill@example.com\">"
jill_two.to_s          # "#<Person @name=\"Jill Smith\", @email=\"jill@example.com\">"
jack.to_s              # "#<Person @name=\"Jack Smith\", @email=\"jack@example.com\">"

jill.with name: "Sue"  # #<Person @name="Sue", @email="jill@example.com">
jill.with bad: "!"     # unknown keyword: :bad (ArgumentError)

As you can see, object equality is determined by the object’s values and not by the object’s identity. When you include Wholeable along with a list of keys, the following happens:

The corresponding public attr_reader (or attr_accessor if mutable) for each key is created which saves you time and reduces double entry when implementing your whole value object.
The #to_a, #to_h, and #to_s methods are added for convenience and to be compatible with Data and Structs.
The #deconstruct and #deconstruct_keys aliases are created so you can leverage pattern matching.
The #==, #eql?, #hash, #inspect, and #with methods are added to provide whole value behavior.
The object is immediately frozen after initialization to ensure your instance is immutable by default.

Initialization

As shown above, you can create an instance of your whole value object by using .[]. Example:

Person[name: "Jill Smith", email: "jill@example.com"]

Alternatively, you can create new instances using .new. Example:

Person.new name: "Jill Smith", email: "jill@example.com"

Both methods work but use .[] when supplying arguments and .new when you don’t have any arguments.

Mutability

All whole value objects are frozen by default. You can change behavior by specifying whether instances should be mutable by passing kind: :mutable as a keyword argument. Example:

class Person
  include Wholeable[:name, :email, kind: :mutable]

  def initialize name: "Jill", email: "jill@example.com"
    @name = name
    @email = email
  end
end

jill = Person.new
jill.frozen? # false

When your object is mutable, you’ll also have access to setter methods in addition to the normal getter methods. Example:

jill.name # "Jill"
jill.name = "Jayne"
jill.name # "Jayne"

You can also make your object immutable by using kind: :immutable but this is default behavior and redundant. Any invalid kind (example: kind: :bogus) will be ignored and default to being immutable.

Inheritance

Unlike Data or Structs, you can subclass a whole value object. Example:

class Person
  include Wholeable[:name]

  def initialize name:
    @name = name
  end
end

class Contact < Person
  include Wholeable[:email]

  def initialize(email:, **)
    super(**)
    @email = email
  end
end

contact = Contact[name: "Jill Smith", email: "jill@example.com"]

contact.to_h     # {name: "Jill Smith", email: "jill@example.com"}
contact.frozen?  # true

Notice Contact inherits from Person while only defining the attributes that make it unique. You don’t need to redefine the same attributes found in the superclass as that would be redundant and defeat the purpose of subclassing in the first place.

When subclassing, each subclass has access to the same attributes defined by the superclass no matter how deep your ancestry is. This does mean you must pass the remaining attributes to the superclass via the double splat.

Mutability is honored but is specific to each object in the ancestry. In other words, if the entire ancestry is immutable then no object can mutate an attribute defined in the ancestry. The same applies if the entire ancestry is mutable except, now, any child can mutate any attribute previously defined by the ancestry. Any attribute that is mutated is only mutated specific to the subclass as is standard inheritance behavior.

If your ancestry is a mixed (immutable and mutable) then behavior is specific to each child in the ancestry. This means a mutable child won’t make the entire ancestry mutable, only the child will be mutable. Best practice is to architect your ancestry so immutability or mutability is the same across all objects. To illustrate, here’s an example with an immutable parent and mutable child:

class Parent
  include Wholeable[:one]

  def initialize one: 1
    @one = one
  end
end

class Child < Parent
  include Wholeable[:two, kind: :mutable]

  def initialize(two: 2, **)
    super(**)
    @two = two
  end
end

child = Child.new

child.one = 100  # NoMethodError
child.two = 200  # 200
child.frozen?    # false

Notice, when attempting to mutate the one attribute, you get a NoMethodError. This is because #one= is defined by the immutable parent while #two= is defined on the mutable child.

If you the flip mutability of your ancestry, you can make your parent mutable while the child immutable for different behavior. Example:

class Parent
  include Wholeable[:one, kind: :mutable]

  def initialize one: 1
    @one = one
  end
end

class Child < Parent
  include Wholeable[:two]

  def initialize(two: 2, **)
    super(**)
    @two = two
  end
end

child = Child.new

child.one = 100  # FrozenError
child.two = 200  # NoMethodError
child.frozen?    # true

In this case, you get a FrozenError for #one= because the parent is mutable and defined the #one= method but the child is immutable which caused the associated attribute to be frozen. On the other hand, the #two= method is never defined by the subclass due to being immutable and so you you get a: NoMethodError.

Again, if using inheritance, ensure immutability or mutability remains consistent throughout the entire ancestry.

Caveats

Whole values can be broken via the following situations:

Post Attributes: Adding additional attributes after what is defined when including Wholeable will break your whole value object. To prevent this, let Wholeable manage this for you (easiest). Otherwise (harder), you can manually override #==, #eql?, #hash, #inspect, #to_a, and #to_h behavior at which point you don’t need Wholeable anymore.
Deep Freezing: The automatic freezing of your instances is shallow and will not deep freeze nested attributes. This behavior mimics the behavior of Data objects.

Performance

The performance of this gem is good but definitely slower than native support for Data and Structs because they are written in C. To illustrate, here’s a micro benchmark for comparison:

INITIALIZATION

ruby 3.3.5 (2024-09-03 revision ef084cc8f4) +YJIT [arm64-darwin23.6.0]
Warming up --------------------------------------
                Data   470.027k i/100ms
              Struct   422.010k i/100ms
               Whole   805.945k i/100ms
Calculating -------------------------------------
                Data      4.750M (± 1.1%) i/s  (210.53 ns/i) -     23.971M in   5.047225s
              Struct      4.579M (± 1.1%) i/s  (218.38 ns/i) -     23.211M in   5.069228s
               Whole      9.408M (± 1.2%) i/s  (106.29 ns/i) -     47.551M in   5.055033s

Comparison:
               Whole:  9407938.7 i/s - 1.60x  slower
                Data:  4750013.8 i/s - 3.17x  slower
              Struct:  4579253.1 i/s - 3.28x  slower

BEHAVIOR

ruby 3.3.5 (2024-09-03 revision ef084cc8f4) +YJIT [arm64-darwin23.6.0]
Warming up --------------------------------------
                Data   129.006k i/100ms
              Struct   129.832k i/100ms
           Wholeable    78.861k i/100ms
Calculating -------------------------------------
                Data      1.336M (± 3.6%) i/s  (748.33 ns/i) -      6.708M in   5.027517s
              Struct      1.341M (± 1.7%) i/s  (745.89 ns/i) -      6.751M in   5.037050s
           Wholeable    816.232k (± 1.9%) i/s    (1.23 μs/i) -      4.101M in   5.025751s

Comparison:
              Struct:  1340687.5 i/s
                Data:  1336304.1 i/s - same-ish: difference falls within error
           Wholeable:   816232.0 i/s - 1.64x  slower

While the above isn’t bad, you can definitely see this gem is slower than Ruby’s own native objects when interacting with it despite being faster upon initialization.

Default to using Data or Structs but, if you find yourself needing a whole value object with more behavior than what a Data or Struct can provide, then this gem is a good solution.

Development

To contribute, run:

git clone https://github.com/bkuhlmann/wholeable
cd wholeable
bin/setup

You can also use the IRB console for direct access to all objects:

bin/console

Tests

To test, run:

bin/rake

Credits

Built with Gemsmith.
Engineered by Brooke Kuhlmann.