attr_extras

Takes some boilerplate out of Ruby, lowering the barrier to extracting small focused classes, without the downsides of using Struct.

Instead of

class InvoiceBuilder
  def initialize(invoice, employee)
    @invoice, @employee = invoice, employee
  end

  private

  attr_reader :invoice, :employee
end

you can just do

class InvoiceBuilder
  pattr_initialize :invoice, :employee
end

This nicely complements Ruby's built-in attr_accessor, attr_reader and attr_writer.

Usage

attr_initialize :foo, :bar
Defines an initializer that takes two arguments and assigns @foo and @bar.

attr_initialize :foo, [:bar, :baz]
Defines an initializer that takes one regular argument, assigning @foo, and one hash argument, assigning @bar and @baz.

attr_private :foo, :bar
Defines private readers for @foo and @bar.

pattr_initialize :foo, :bar
Defines both initializer and private readers.

attr_value :foo, :bar
Defines both initializer and public readers.

method_object :fooable?, :foo
Defines a .fooable? class method that delegates to an instance method.

attr_id_query :foo?, :bar?
Defines query methods like foo?, which is true iff foo_id is truthy. Goes well with Active Record.

attr_query :foo?, :bar?
Defines query methods like foo?, which is true iff foo is truthy.

Findability has been a central consideration. Hence the long name attr_initialize, so you see it when scanning for the initializer; and the enforced questionmarks with attr_id_query :foo?, so you can search for that method.

Example

class MyClass
  attr_initialize :foo, :bar
  attr_private :foo
  attr_id_query :item?
  attr_query :oof?

  def oof
    foo.reverse
  end

  def item_id
    123
  end
end

x = MyClass.new("Foo!", "Bar!")
x.oof    # => "!ooF"
x.foo    # NoMethodError: private method `foo' called.
x.item?  # => true
x.oof?   # => true

class MyMethodObject
  method_object :fooable?,
    :foo

  def fooable?
    foo == :some_value
  end
end

MyMethodObject.fooable?(:some_value)     # => true
MyMethodObject.fooable?(:another_value)  # => false

class MyHashyObject
  attr_initialize :foo, [:bar, :baz]
  attr_reader :bar
end

x = MyHashyObject.new("Foo!", bar: "Bar!", baz: "Baz!")
x.bar  # => "Bar!"

class MyValueObject
  attr_value :foo, :bar
end

x = MyValueObject.new(5, 10)
x.foo # => 5
x.bar # => 10
x.foo = 20 # NoMethodError: undefined method `foo=''`

Why not use `Struct`?

See: "Struct inheritance is overused"

Why not use `private; attr_reader :foo`?

Instead of attr_private :foo, you could do private; attr_reader :foo.

Other than being more to type, declaring attr_reader after private will actually give you a warning (deserved or not) if you run Ruby with warnings turned on.

If you don't want the dependency on attr_extras, you can get rid of the warnings with attr_reader :foo; private :foo or just define a regular private method.

Installation

Add this line to your application's Gemfile:

gem "attr_extras"

And then execute:

bundle

Or install it yourself as:

gem install attr_extras

License

MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.