mattr_accessor
mattr_accessor(*syms, instance_reader: true, instance_writer: true, instance_accessor: true, default: nil, &blk)
public
Defines both class and instance accessors for class attributes. All class and instance methods created will be public, even if this method is called with a private or protected access modifier.
module HairColors mattr_accessor :hair_colors end class Person include HairColors end HairColors.hair_colors = [:brown, :black, :blonde, :red] HairColors.hair_colors # => [:brown, :black, :blonde, :red] Person.new.hair_colors # => [:brown, :black, :blonde, :red]
If a subclass changes the value then that would also change the value for parent class. Similarly if parent class changes the value then that would change the value of subclasses too.
class Male < Person end Male.new.hair_colors << :blue Person.new.hair_colors # => [:brown, :black, :blonde, :red, :blue]
To opt out of the instance writer method, pass instance_writer: false. To opt out of the instance reader method, pass instance_reader: false.
module HairColors mattr_accessor :hair_colors, instance_writer: false, instance_reader: false end class Person include HairColors end Person.new.hair_colors = [:brown] # => NoMethodError Person.new.hair_colors # => NoMethodError
Or pass instance_accessor: false, to opt out both instance methods.
module HairColors mattr_accessor :hair_colors, instance_accessor: false end class Person include HairColors end Person.new.hair_colors = [:brown] # => NoMethodError Person.new.hair_colors # => NoMethodError
You can set a default value for the attribute.
module HairColors mattr_accessor :hair_colors, default: [:brown, :black, :blonde, :red] end class Person include HairColors end Person.class_variable_get("@@hair_colors") # => [:brown, :black, :blonde, :red]