Optional Attributes and Default Values
By default both params and options are mandatory. Use :default key to make them optional:
require 'dry-initializer'
class User
extend Dry::Initializer
param :name, default: proc { 'Unknown user' }
option :email, default: proc { 'unknown@example.com' }
option :phone, optional: true
end
user = User.new
user.name # => 'Unknown user'
user.email # => 'unknown@example.com'
user.phone # => Dry::Initializer::UNDEFINED
user = User.new 'Vladimir', email: 'vladimir@example.com', phone: '71234567788'
user.name # => 'Vladimir'
user.email # => 'vladimir@example.com'
user.phone # => '71234567788'
You cannot define required parameter after optional one. The following example raises SyntaxError exception:
require 'dry-initializer'
class User
extend Dry::Initializer
param :name, default: proc { 'Unknown name' }
param :email # => #<SyntaxError ...>
end
You should assign nil value explicitly. Otherwise an instance variable will be left undefined. In both cases attribute reader method will return nil.
require 'dry-initializer'
class User
extend Dry::Initializer
param :name
option :email, optional: true
end
user = User.new 'Andrew'
user.email # => nil
user.instance_variable_get :@email
# => Dry::Initializer::UNDEFINED
user = User.new 'Andrew', email: nil
user.email # => nil
user.instance_variable_get :@email
# => nil
You can also set nil as a default value:
require 'dry-initializer'
class User
extend Dry::Initializer
param :name
option :email, default: proc { nil }
end
user = User.new 'Andrew'
user.email # => nil
user.instance_variable_get :@email
# => nil
You must wrap default values into procs.
If you need to assign proc as a default value, wrap it to another one:
require 'dry-initializer'
class User
extend Dry::Initializer
param :name_proc, default: proc { proc { 'Unknown user' } }
end
user = User.new
user.name_proc.call # => 'Unknown user'
Proc will be executed in a scope of new instance. You can refer to other arguments:
require 'dry-initializer'
class User
extend Dry::Initializer
param :name
param :email, default: proc { "#{name.downcase}@example.com" }
end
user = User.new 'Andrew'
user.email # => 'andrew@example.com'