variables

Variable objects for class and instance variables

Ruby already has Method objects, why not Variable objects as well?

Installation

gem install variables

Requirements

Ruby 1.8.7+

Usage

Let's experiment with a simple User class.

class User
  def initialize(name)
    @name = name
  end
end

Objects can have any number of instance variables.

user = User.new('Bob')              #=> #<User:0x007f8f6a84aa98>
user.instance_variable_get('@name') #=> "Bob"

Similar to Object#method, a handy instance_variable method is available for us to use.

name = user.instance_variable(:name) #=> #<InstanceVariable: #<User>@name>

But unlike Object#method, this method does not require a variable to actually be defined.

undefined = user.instance_variable(:undefined) #=> #<InstanceVariable: #<User>@undefined>

We can check if a variable is defined by using the defined? method.

name.defined?      #=> true
undefined.defined? #=> false

Once we have a Variable object, we can get its value.

name.get      #=> "Bob"
undefined.get #=> nil

Similar to Hash#fetch, the fetch method raises an exception if the variable is undefined.

name.fetch      #=> "Bob"
undefined.fetch #=> Variables::UndefinedVariable - undefined variable "undefined"

The fetch method optionally accepts a default value to return if the variable is undefined.

name.fetch(:default)      #=> "Bob"
undefined.fetch(:default) #=> :default

Default values can also be defined with a block which is yielded the Variable name.

name.fetch { |name| "#{name}-default" }      #=> "Bob"
undefined.fetch { |name| "#{name}-default" } #=> "@undefined-default"

We can update a Variable value by using the set method.

name.set('Steve')                   #=> "Steve"
user.instance_variable_get('@name') #=> "Steve"

The replace method is similar to set, but it returns the old value instead of the new value.

name.replace('Bob')                 #=> "Steve"
user.instance_variable_get('@name') #=> "Bob"

We can even temporarily replace a value for the duration of a block.

user.instance_variable_get('@name') #=> "Bob"

value = name.replace('Steve') do
  user.instance_variable_get('@name') #=> "Steve"

  'we can return a value here'
end

user.instance_variable_get('@name') #=> "Bob"

value.inspect #=> "we can return a value here"

Everything that we do with instance variables can be done with class variables as well!

example = User.class_variable(:example) #=> #<ClassVariable: User@@name>

example.defined? #=> false

example.set('testing') #=> "testing"

User.class_variable_get('@@example') #=> "testing"

Testing

bundle exec rspec

Contributing