basics of metaprogramming in ruby
DESCRIPTION
budapest ruby meetup, 10/2013 Tamas TompaTRANSCRIPT
Basics of MetaprogrammingTamás Tompa (Digital Natives)
Budapest Ruby Meetup 2013
02/10/2013
Thursday, October 3, 13
“Metaprogramming is writing code that writes code.”
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what for?§ examples
§ writing a wrapper§ DSL (domain specific language)§ keep your code DRY§ extend core ruby classes
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runtime§ static vs dynamic metaprogramming§ everything is object (even classes)§ code introspection
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well known example§ ActiveRecord::Base
§ reads the schema at runtime§ discovers fields§ conventions
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monkey patching§ monkey patch is a way to extend or
modify the run-time code of dynamic languages without altering the original source code
§ can be dangerous§ always carefully check the existing
methods
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basicsobj = MyClass.newobj.class # => MyClass
"hello".class # => StringString.class # => Class
obj.instance_variables # => [:@v]
obj.methods.grep(/my/) # => [:my_method]
Class.instance_methods(false)
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basics# ignore inherited methodsClass.instance_methods(false)
String.superclass # => ObjectObject.superclass # => BasicObjectBasicObject.superclass # => nil
# module and kernelD.ancestors # => [D, C, M, Object, Kernel, BasicObject]
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“Classes themselves are nothing but objects.”
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object model
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dynamic methodsclass MyClass
define_method :my_method do |my_arg|
my_arg * 3
end
end
obj = MyClass.new
obj.my_method(2) # => 6
obj.send(:my_method, 2) # => 6
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generating methodsclass Computer
def initialize(computer_id, data_source)
end
def self.define_component(name)
define_method(name) do
info = @data_source.send "get_#{name}_info" , @id
price = @data_source.send "get_#{name}_price" , @id
end
end
define_component :mouse
define_component :cpu
end
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method missingclass Lawyer
def method_missing(method, *args)
puts "You called: #{method}(#{args.join(', ')})"
puts "(You also passed it a block)" if block_given?
end
end
bob = Lawyer.new
bob.talk_simple('a' , 'b' ) do
# a block
end
You called: talk_simple(a, b)
(You also passed it a block)
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http://pragprog.com/book/ppmetr/metaprogramming-ruby
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We’re hiring!http://digitalnatives.hu/jobs
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