Subclass

The Subclass mixin is used to define subclasses with partially applied constructor parameters.

class Character
  extend SleepingKingStudios::Tools::Toolbox::Subclass

  def initialize(*traits, **attributes)
    @attributes = @attributes
    @traits     = traits
  end

  attr_reader :attributes

  attr_reader :traits
end

Bard = Character.subclass(:charismatic, :musical)

aoife = Bard.new(:sorcerous)
aoife.traits
#=> [:charismatic, :musical, :sorcerous]

The class reference for SleepingKingStudios::Tools::Toolbox::Subclass can be found in Reference.

Contents

• Custom Subclasses
  • Constructor Arguments
  • Constructor Keywords
  • Constructor Block

Custom Subclasses

Add Subclass mixin to a Class to enable defining custom subclasses.

class Character
  extend SleepingKingStudios::Tools::Toolbox::Subclass

  def initialize(*traits)
    @traits = traits
  end

  attr_reader :traits
end

The .subclass(*arguments, **keywords, &block) class method defines a new subclass, and the given parameters will be applied when calling .new on the defined subclass.

Bard = Character.subclass(:charismatic, :musical)

Constructor Arguments

Arguments passed to .subclass() are prepended to the arguments array when instantiating the subclass.

fighter = Character.new(:armored, :strong)
fighter.traits
#=> [:armored, :strong]

Bard = Character.subclass(:charismatic, :musical)
bard = Bard.new
bard.traits
#=> [:charismatic, :musical]

aoife = Bard.new(:sorcerous)
aoife.traits
#=> [:charismatic, :musical, :sorcerous]

In the above example, the arguments :charismatic and :musical are passed from the Bard subclass, after which :sorcerous is passed from Bard.new.

Constructor Keywords

The keywords hash is merged into any keywords passed to .subclass() when instantiating the subclass.

fighter = Character.new(might: 5, magic: 1, mind: 3)
fighter.attributes
#=> { might: 5, magic: 1, mind: 3 }

MageKnight  = Character.subclass(might: 4, magic: 3)
mage_knight = MageKnight.new(magic: 5, mind: 2)
mage_knight.attributes
#=> { might: 4, magic: 5, mind: 2 }

In the above example, the keywords might: 4 and magic: 3 are passed from the MageKnight subclass, while magic: 5 and mind: 2 are passed from MageKnight.new. The magic: 5 passed directly to the constructor overrides the value from the subclass.

Constructor Block

If a block is passed to .subclass(), that block will be passed when instantiating the subclass, unless another block is passed to #initialize.

class Greeter
  def initialize(&block)
    @block = block
  end

  def greet
    @block.call
  end
end

Greeter.new { puts 'Greetings, programs!' }.greet
#=> writes "Greetings, programs!" to STDOUT

SpaceGreeter = Greeter.subclass { puts 'Greetings, starfighter!' }
SpaceGreeter.new.greet
#=> writes "Greetings, starfighter!" to STDOUT

SpaceGreeter.new { puts 'Greetings, programs!' }.greet
#=> writes "Greetings, programs!" to STDOUT

In the above example, the SpaceGreeter will print "Greetings, starfighter!" to STDOUT unless another block is passed to the constructor.

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