Ruby Metaprogramming
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Thaichor Seng is a junior developer currently working on a restaurant menu application using Ruby on Rails. The document discusses metaprogramming in Ruby, which is writing code that writes code. It provides examples of metaprogramming methods like define_method(), method_missing(), class_eval(), and eval(). These methods allow dynamically adding methods to classes at runtime rather than during class definition.
![class Currency
def initialize(value)
@value = value
end
[:usd, :riel, :yen, :bat].each do |method|
define_method ¡°to_#{method}¡± do
¡°#{@value.to_s} #{method.to_s}¡±
end
end
end
c = Currency.new(14)
c.to_usd # 14 usd
c.to_riel # 14 riel](https://image.slidesharecdn.com/rubymetaprogramming-121216080713-phpapp02/85/Ruby-Metaprogramming-6-320.jpg)
![class MyOpenStruct
def initialize
@attributes = {}
end
def method_missing(name, *args)
attribute = name.to_s
if attribute =~ /=$/
@attributes[attribute.chop] = args[0]
else
@attributes[attribute]
end
end
end
icecream = MyOpenStruct.new
icecream.flavor = "vanilla¡° # nil
icecream.flavor # vanilla](https://image.slidesharecdn.com/rubymetaprogramming-121216080713-phpapp02/85/Ruby-Metaprogramming-9-320.jpg)
![map = { "update" => "deploy:update" ,
"restart" => "deploy:restart" ,
"cleanup" => "deploy:cleanup" }
map.each do |old, new|
eval "task(#{old.inspect}) do
warn "[DEPRECATED] `#{old}' is deprecated. Use `#{new}' instead."
find_and_execute_task(#{new.inspect})
end"
end](https://image.slidesharecdn.com/rubymetaprogramming-121216080713-phpapp02/85/Ruby-Metaprogramming-11-320.jpg)
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Ruby Metaprogramming
- 2. Name: Thaichor Seng Position: Junior Developer at Yoolk.Inc I?m currently working on creating Restaurant Menu application using Ruby on Rails.
- 3. ? Sugar Syntax ? Dynamic Language ? English Like ? Lots of built-in methods ? Metaprogramming
- 4. Metaprogramming is writing code that writes code. Here are some method using for metaprogramming: ? define_method() ? method_missing() ? class_eval() ? eval()
- 5. class MyClass define_method :my_method do |my_arg| my_arg * 3 end # def my_method(my_arg) # my_arg * 3 # end end obj = MyClass.new obj.my_method(2) # => 6
- 6. class Currency def initialize(value) @value = value end [:usd, :riel, :yen, :bat].each do |method| define_method ¡°to_#{method}¡± do ¡°#{@value.to_s} #{method.to_s}¡± end end end c = Currency.new(14) c.to_usd # 14 usd c.to_riel # 14 riel
- 7. class Lawyer end nick = Lawyer.new nick.talk_simple NoMethodError: undefined method ?talk_simple' for #<Lawyer:0x3c848>
- 8. class Lawyer def method_missing(method, *args) puts "You called: #{method}(#{args.join(', ')})" end end nick = Lawyer.new nick.talk_simple # You called talk_simple() Nick.talk(a, b) # You called talk(a, b)
- 9. class MyOpenStruct def initialize @attributes = {} end def method_missing(name, *args) attribute = name.to_s if attribute =~ /=$/ @attributes[attribute.chop] = args[0] else @attributes[attribute] end end end icecream = MyOpenStruct.new icecream.flavor = "vanilla¡° # nil icecream.flavor # vanilla
- 10. def add_method_to(a_class) a_class.class_eval do def m 'Hello!' end end end add_method_to String "abc".m # => "Hello!¡°
- 11. map = { "update" => "deploy:update" , "restart" => "deploy:restart" , "cleanup" => "deploy:cleanup" } map.each do |old, new| eval "task(#{old.inspect}) do warn "[DEPRECATED] `#{old}' is deprecated. Use `#{new}' instead." find_and_execute_task(#{new.inspect}) end" end
- 12. The End