dememoize

Description

dememoize is a gem that provides a way to remove a memoized value (an instance variable) from a class or an object instance.

The primary use case is usage in spec tests. If you have a code that memoizes a value, but you would like to check that the value is calculated differently under different circumstances, you can use dememoize to remove the memoized value, leaving you free to add another spec that can check the value again. There are rspec shared contexts that can help you with this.

eg:

class Product
  class << self 
    def categories
      @categories ||= expensive_calculation
    end
  end
end

describe "test different memoized values based on environment" do
  # Here is the shared_context that dememoize provides that aids with the specs
  include_context "with dememoized class variable", :@categories
  
  it "should return one value for prelive" do
    expect(Rails).to receive(:env).and_return("prelive")
    expect(Product.categories).to eq(1)
  end
  
  it "should return another value for production" do
    expect(Rails).to receive(:env).and_return("production")
    expect(Product.categories).to eq(2)
  end
end

Installation

Add this line to your application's Gemfile, probably in the :test group:

group :test do
  gem "dememoize"
end

Simple usage

You can dememoize an instance:

class Car
  def bolts
    @bolts ||= expensive_calculation
  end
end

car = Car.new
car.bolts # => 28376
car.dememoize(:@bolts)
car.instance_variable_defined?(:@bolts) # => false

# You can also specify the instance variable name as a string
car.bolts # => 28376
car.dememoize("@bolts")
car.instance_variable_defined?(:@bolts) # => false

You can dememoize a class variable:

class Product
  class << self
    def categories
      @categories ||= expensive_calculation
    end
  end
end

Product.categories # => 4324
Product.dememoize(:@categories)
Product.instance_variable_defined?(:@categories) # => false

Usage with RSpec

dememoize comes with rspec context helpers to dememoize a class variable in a spec:

# In this example, dememoize assumes that the class under test is the object that should have the
# class instance variable removed.
describe "without specifying a class it uses described_class" do
  include_context "with dememoized class variable", :@categories
  
  it "should return one value for prelive" do
    expect(Rails).to receive(:env).and_return("prelive")
    expect(Product.categories).to eq(1234)
  end
  
  it "should return another value for production" do
    expect(Rails).to receive(:env).and_return("production")
    expect(Product.categories).to eq(5678)
  end
end

# If you want to dememoize a class variable on a different class, you can pass the class as the
# first argument to dememoized.

describe "specify a different class (Bar) to dememoize" do
  include_context "with dememoized class variable", :@categories, clazz: Bar # <-- Bar is the class
  # ...
end

Upgrading

dememoize uses semantic versioning, so major version changes will usually require additional actions to be taken upgrading from one major version to another.

Changelog

A full changelog can be found here: CHANGELOG.md