instance method
mattr_reader
Ruby on Rails 7.0.10
Signature
mattr_reader(*syms, instance_reader: true, instance_accessor: true, default: nil, location: nil)Defines a class attribute and creates a class and instance reader methods. The underlying class variable is set to nil, if it is not previously defined. 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_reader :hair_colors
end
HairColors.hair_colors # => nil
HairColors.class_variable_set("@@hair_colors", [:brown, :black])
HairColors.hair_colors # => [:brown, :black]
The attribute name must be a valid method name in Ruby.
module Foo
mattr_reader :"1_Badname"
end
# => NameError: invalid attribute name: 1_Badname
To omit the instance reader method, pass instance_reader: false or instance_accessor: false.
module HairColors
mattr_reader :hair_colors, instance_reader: false
end
class Person
include HairColors
end
Person.new.hair_colors # => NoMethodError
You can set a default value for the attribute.
module HairColors
mattr_reader :hair_colors, default: [:brown, :black, :blonde, :red]
end
class Person
include HairColors
end
Person.new.hair_colors # => [:brown, :black, :blonde, :red]
Parameters
-
symsrest -
instance_readerkey = true -
instance_accessorkey = true -
defaultkey = nil -
locationkey = nil
Source
# File activesupport/lib/active_support/core_ext/module/attribute_accessors.rb, line 53
def mattr_reader(*syms, instance_reader: true, instance_accessor: true, default: nil, location: nil)
raise TypeError, "module attributes should be defined directly on class, not singleton" if singleton_class?
location ||= caller_locations(1, 1).first
definition = []
syms.each do |sym|
raise NameError.new("invalid attribute name: #{sym}") unless /\A[_A-Za-z]\w*\z/.match?(sym)
definition << "def self.#{sym}; @@#{sym}; end"
if instance_reader && instance_accessor
definition << "def #{sym}; @@#{sym}; end"
end
sym_default_value = (block_given? && default.nil?) ? yield : default
class_variable_set("@@#{sym}", sym_default_value) unless sym_default_value.nil? && class_variable_defined?("@@#{sym}")
end
module_eval(definition.join(";"), location.path, location.lineno)
end
Defined in activesupport/lib/active_support/core_ext/module/attribute_accessors.rb line 53
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