Ruby Metaprogramming

RUBY META PROGRAMMING.

@fnando

AVISOS.

TUDO É OBJETO. INCLUINDO CLASSES.

MUITO CÓDIGO.

VARIÁVEIS DE CLASSE.

class MyLib @@name = "mylib" def self.name @@name end end

MyLib.name #=> “mylib”

class MyOtherLib < MyLib @@name = "myotherlib" end

MyOtherLib.name #=> “myotherlib” MyLib.name #=> “myotherlib”

VARIÁVEIS DE CLASSE SÃO COMPARTILHADAS.

VARIÁVEIS DE INSTÂNCIA.

class MyLib @name = "mylib" def self.name @name end end

MyLib.name #=> “mylib”

class MyOtherLib < MyLib @name = "myotherlib" end

MyOtherLib.name #=> “myotherlib” MyLib.name #=> “mylib”

VARIÁVEIS DE INSTÂNCIA PERTENCEM AO OBJETO.

METACLASSE.

class MyLib class << self end end

class MyLib # ruby 1.9.2+ singleton_class.class_eval do end end

class Object def singleton_class class << self; self; end end end unless Object.respond_to?(:singleton_class)

class MyLib class << self attr_accessor :name end end

MyLib.name = "mylib" MyLib.name #=> mylib

BLOCOS.

MÉTODOS PODEM RECEBER BLOCOS.

def run(&block) end

BLOCOS PODEM SER EXECUTADOS.

def run(&block) yield arg1, arg2 end

def run(&block) block.call(arg1, arg2) end

def run(&block) block[arg1, arg2] end

def run(&block) # ruby 1.9+ block.(arg1, arg2) end

METACLASSE, BLOCOS E VARIÁVEL DE INSTÂNCIA.

MyLib.configure do |config| config.name = "mylib" end

class MyLib class << self attr_accessor :name end def self.configure(&block) yield self end end

EVALUATION.

eval, class_eval, e instance_eval

MyLib.class_eval <<-RUBY "running inside class" RUBY #=> “running inside class”

MyLib.class_eval do "running inside class" end #=> “running inside class”

handler = proc { self.kind_of?(MyLib) } handler.call #=> false

handler = proc { self.kind_of?(MyLib) } lib.instance_eval(&handler) #=> true

BLOCOS, METACLASSE, VARIÁVEIS DE INSTÂNCIA, EVALUATION.

MyLib.configure do self.name = "mylib" name #=> “mylib” end

class MyLib class << self attr_accessor :name end def self.configure(&block) instance_eval(&block) end end

DEFINIÇÃO DE MÉTODOS.

MONKEY PATCHING.

class Integer def kbytes self * 1024 end end 128.kbytes #=> 131072

deﬁne_method.

MyLib.class_eval do define_method "name" do @name end define_method "name=" do |name| @name = name end end

lib = MyLib.new lib.name = "mynewname" lib.name #=> “mynewname”

EVALUATION.

MyLib.class_eval <<-RUBY def self.name "mylib" end def name "mylib's instance" end RUBY

MyLib.class_eval do def self.name "mylib" end def name "mylib's instance" end end

MyLib.name #=> “mylib” MyLib.new.name #=> “mylib’s instance”

BLOCOS, EVALUATION, DEFINIÇÃO DE MÉTODOS.

MyLib.class_eval do name "mylib" name #=> “mylib” end

class MyLib def self.accessor(method) class_eval <<-RUBY def self.#{method}(*args) if args.size.zero? @#{method} else @#{method} = args.last end end RUBY end accessor :name end

MyLib.class_eval do name "mylib" name #=> “mylib” end

configure do name "mylib" name #=> “mylib” end

def configure(&block) MyLib.instance_eval(&block) end

DISCLAIMER.

METHOD MISSING.

MyLib.new.invalid

NoMethodError: undefined method ‘invalid’ for #<MyLib:0x10017e2f0>

class MyLib NAMES = { :name => "mylib’s instance" } def method_missing(method, *args) if NAMES.key?(method.to_sym) NAMES[method.to_sym] else super end end end

class MyLib #... def respond_to?(method, include_private = false) if NAMES.key?(method.to_sym) true else super end end end

lib.name #=> “mylib’s instance” lib.respond_to?(:name) #=> true

MIXINS.

class MyLib extend Accessor accessor :name end class MyOtherLib extend Accessor accessor :name end

module Accessor def accessor(name) class_eval <<-RUBY def self.#{name}(*args) if args.size.zero? @#{name} else @#{name} = args.last end end RUBY end end

MONKEY PATCHING, MIXINS, EVALUATION, DYNAMIC DISPATCHING E HOOKS.

class Conference < ActiveRecord::Base has_permalink end

"welcome to QConSP".to_permalink #=> “welcome-to-qconsqp”

class String def to_permalink self.downcase.gsub(/[^[a-z0-9]-]/, "-") end end

class Conference < ActiveRecord::Base before_validation :generate_permalink def generate_permalink write_attribute :permalink, name.to_s.to_permalink end end

module Permalink end ActiveRecord::Base.send :include, Permalink

module Permalink def self.included(base) base.send :extend, ClassMethods end end

module Permalink # ... module ClassMethods def has_permalink class_eval do before_validation :generate_permalink include InstanceMethods end end end end

module Permalink # ... module InstanceMethods def generate_permalink write_attribute :permalink, name.to_s.to_permalink end end end

conf = Conference.create(:name => "QConSP 2010") conf.permalink #=> "qconsp-2010"

ENTÃO...

META PROGRAMMING É COMPLICADO.

MAS NEM TANTO.

APRENDA RUBY.

OBRIGADO.

nandovieira.com.br simplesideias.com.br spesa.com.br github.com/fnando @fnando

Ruby Metaprogramming

by Nando Vieira on Sep 12, 2010

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Ruby Metaprogramming — Presentation Transcript