class SimpleFlag

Class FeatureFlag defines and stores feature flags

@example Configuration

FEATURE = FeatureFlag.new do |feature|
  feature.define(:new_user_profile) do |user_id:|
    Admin.where(user_id: user_id).exists?
  end

  feature.define(:third_party_analytics) do
    not Rails.env.production?
  end
end

@example Usage

class ProfilesController < ApplicationController
  def show
    FEATURE.with(:new_user_profile, user_id: current_user.id) do
      return render :new_user_profile, locals: { user: NewUserProfilePresenterV2.new(current_user) }
    end

    render :show, locals: { user: UserProfilePresenterV1.new(current_user) }
  end
end

@example Testing with before…after

describe "User profiles" do
  before { FEATURE.override(:new_user_profile, true) }
  after  { FEATURE.reset_all_overrides }
end

@example Testing with inline block

it "shows new user profile" do
  FEATURE.override_with(:new_user_profile, true) do
    expect( FEATURE.active?(:new_user_profile) ).to be_truthy
  end

  expect( FEATURE.active?(:new_user_profile) ).to be_falsy
end

@see blog.arkency.com/2015/11/simple-feature-toggle-for-rails-app/

Constants

FlagAlreadyDefined
FlagArgumentsMismatch
FlagNotDefined
FlagNotOverridden
VERSION

Attributes

env[R]

Public Class Methods

new(env: nil) { |self| ... } click to toggle source

# File lib/simple_flag.rb, line 58
def initialize(env: nil)
  @env       = env
  @flags     = {}
  @overrides = {}
  yield self if block_given?
end

Public Instance Methods

active?(name, *args) click to toggle source

# File lib/simple_flag.rb, line 130
def active?(name, *args)
  flag = @flags.fetch(name, proc { |*_args| false })
  validate_flag_arguments(name, flag.arity, args.size)
  flag.call(*args)
end

Also aliased as: enabled?

define(name, &block) click to toggle source

# File lib/simple_flag.rb, line 65
def define(name, &block)
  raise FlagAlreadyDefined, "Feature flag `#{name}` is already defined" if flag?(name)

  @flags[name] = block
end

disabled?(name, *args)

Alias for: inactive?

enabled?(name, *args)

Alias for: active?

env?(*args) click to toggle source

# File lib/simple_flag.rb, line 142
def env?(*args)
  [*args].map(&:to_s).include?(env.to_s)
end

flag?(name) click to toggle source

# File lib/simple_flag.rb, line 122
def flag?(name)
  @flags.key?(name)
end

flags() click to toggle source

# File lib/simple_flag.rb, line 75
def flags
  @flags.keys
end

inactive?(name, *args) click to toggle source

# File lib/simple_flag.rb, line 137
def inactive?(name, *args)
  !active?(name, *args)
end

Also aliased as: disabled?

overridden?(name) click to toggle source

# File lib/simple_flag.rb, line 126
def overridden?(name)
  @overrides.key?(name)
end

override(name, result = true, &block) click to toggle source

# File lib/simple_flag.rb, line 83
def override(name, result = true, &block)
  raise FlagNotDefined, "Feature flag `#{name}` is not defined" unless flag?(name)
  raise FlagAlreadyDefined, "Feature flag `#{name}` is already overridden" if overridden?(name)

  # We are using proc, not lambda, because proc does not check for number of arguments
  original_block = @flags[name]
  @overrides[name] = original_block
  @flags[name] =
    if block_given?
      validate_flag_arity(name, original_block.arity, block.arity)
      block
    else
      proc { |*_args| result }
    end

  original_block
end

override_with(name, result = true, &block) click to toggle source

# File lib/simple_flag.rb, line 112
def override_with(name, result = true, &block)
  raise FlagNotDefined, "Feature flag `#{name}` is not defined" unless flag?(name)

  original_block = @flags[name]
  @flags[name] = proc { |*_args| result }
  block.call
ensure
  @flags[name] = original_block
end

redefine(name, &block) click to toggle source

# File lib/simple_flag.rb, line 71
def redefine(name, &block)
  @flags[name] = block
end

reset_all_overrides() click to toggle source

# File lib/simple_flag.rb, line 108
def reset_all_overrides
  @overrides.each_key { |name| reset_override(name) }
end

reset_override(name) click to toggle source

# File lib/simple_flag.rb, line 101
def reset_override(name)
  raise FlagNotOverridden, "Feature flag `#{name}` was not overridden" unless overridden?(name)

  original_block = @overrides.delete(name)
  @flags[name] = original_block
end

with(name, *args, &block) click to toggle source

# File lib/simple_flag.rb, line 79
def with(name, *args, &block)
  block.call if active?(name, *args)
end

Private Instance Methods

validate_flag_arguments(flag_name, flag_arity, args_size) click to toggle source

# File lib/simple_flag.rb, line 157
def validate_flag_arguments(flag_name, flag_arity, args_size)
  if flag_arity < 0 && (flag_arity.abs - 1) > args_size
    # Contains variable -n-1 arguments
    raise FlagArgumentsMismatch, "Flag '#{flag_name}' expects #{flag_arity.abs - 1} or more arguments, " \
          "but #{args_size} arguments were given"
  elsif flag_arity >= 0 && flag_arity != args_size
    # Contains zero or fixed number of arguments
    raise FlagArgumentsMismatch, "Flag '#{flag_name}' expects #{flag_arity} arguments, " \
          "but #{args_size} arguments were given"
  end
end

validate_flag_arity(flag_name, flag_arity, override_arity) click to toggle source

# File lib/simple_flag.rb, line 148
def validate_flag_arity(flag_name, flag_arity, override_arity)
  original_arity = flag_arity < 0 ? flag_arity.abs - 1 : flag_arity

  if original_arity != override_arity
    raise FlagArgumentsMismatch, "Flag '#{flag_name}' expects #{flag_arity} arguments, " \
          "but #{override_arity} arguments were given"
  end
end