This README is the one indexed from the repository at its latest ref, not from the tag for this version.

Metaclass

A Crystal library for manipulating class-level definitions.

Installation

Add this to your application's shard.yml:

dependencies:
  metaclass:
    github: mosop/metaclass

Features

Class Property

require "metaclass/object"

class Misc
  metaclass!
  class_getter faces = {:smile => ":)", :frown => ":("}
  class_setter passcode = Random.rand(10000)
  class_property movie = "Jaws"
end

Misc.faces # => {:smile => ":)", :frown => ":("}
Misc.faces = {:smile => ":D", :frown => ":{"} # raises error (getter only)
Misc.passcode = Random.rand(10000)
Misc.passcode # raises error (setter only)
Misc.movie # => "Jaws"
Misc.movie = "La Strada"
Misc.movie # => "La Strada"

Predicate

require "metaclass/object"

class Misc
  metaclass!
  class_getter? exists = true
  class_setter? promise_broken = false
  class_property? happy = false, neg: unhappy
end

Misc.exists? # => true
Misc.exists! # => raises error (getter only)
Misc.promise_broken!
Misc.promise_broken? # raises error (setter only)
Misc.happy? # => false
Misc.happy!
Misc.happy? # => true
Misc.unhappy!
Misc.happy? # => false

Computed Property

require "metaclass/object"

class Constant
  metaclass!
  class_getter uuid : String { SecureRandom.uuid }
end

class Inconstant
  metaclass!
  class_getter uuid : String, memo: false { SecureRandom.uuid }
end

Constant.uuid == Constant.uuid # => true
Inconstant.uuid != Inconstant.uuid # => true

Variable Inheritance

require "metaclass/object"

class A
  metaclass!
  class_getter inheritance, Hash(Symbol, String) do
    {:a => "a"}
  end
end

class B < A
  metaclass!
  inherited_class_getter inheritance do |parent|
    parent.merge(:b => "b")
  end
end

A.inheritance # => {:a => "a"}
B.inheritance # => {:a => "a", :b => "b"}

Usage

require "metaclass/object"

class A
  metaclass!
end

Or more clean:

require "metaclass"

class A
  Metaclass.metaclass!
end

And see Features

Release Notes

• v0.1.1
  • Predicate

Contributing

1. Fork it ( https://github.com/mosop/metaclass/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes (git commit -am 'Add some feature')
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• mosop - creator, maintainer