mattr_writer

mattr_writer(*syms)

Instance Public methods

Defines a class attribute and creates a class and instance writer methods to allow assignment to the attribute.

module HairColors
  mattr_writer :hair_colors
end
 
class Person
  include HairColors
end
 
HairColors.hair_colors = [:brown, :black]
Person.class_variable_get("@@hair_colors") # => [:brown, :black]
Person.new.hair_colors = [:blonde, :red]
HairColors.class_variable_get("@@hair_colors") # => [:blonde, :red]

If you want to opt out the instance writer method, pass instance_writer: false or instance_accessor: false.

module HairColors
  mattr_writer :hair_colors, instance_writer: false
end
 
class Person
  include HairColors
end
 
Person.new.hair_colors = [:blonde, :red] # => NoMethodError

Also, you can pass a block to set up the attribute with a default value.

class HairColors
  mattr_writer :hair_colors do
    [:brown, :black, :blonde, :red]
  end
end
 
class Person
  include HairColors
end
 
Person.class_variable_get("@@hair_colors") # => [:brown, :black, :blonde, :red]

cattr_writer

Links:

https://github.com/rails/rails/blob/c758093eca303704f52b45fd0660e13600b9b315/activesupport/lib/active_support/core_ext/module/attribute_accessors.rb#L119

doc_ruby_on_rails

2025-01-10 15:47:30

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