最近的Ruby for Rails读书笔记-优快云博客

本文介绍了Ruby中的元编程技术，包括使用class<< self定义类方法、利用self.included和self.inherited作为模块或类继承的hook、通过const_missing处理未定义常量、运用eval和Proc进行动态执行等高级特性。

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1, 用"class <<"定义class method
[code]
class User < ActiveRecord::Base

class << self
def authenticate(username, password)
find_by_username(username, :conditions => [password_hash = ?", Digest::SHA1.hexdigest(passwword)])
end
[/code]

2, 用self.included(class)方法作为include模块的hooks
[code]
module M
def self.included(c)
puts "I have just been mixed into #{c}."
end
end

class C
include M
end
[/code]

3, 用self.inherited(subclass)作为class继承的hooks
[code]
class C
def self.inherited(subclass)
puts "#{self} just got subclassed by #{subclass}"
end
end

class D < C
end
[/code]
用self.const_missing(const)作为class缺失const的hooks
[code]
class C
def self.const_missing(const)
puts "#{const} is undefined-setting it to 1."
const_set(const, 1)
end
end

puts C::A
[/code]

4, 用eval/instance_eval/class_eval(module_eval)动态执行程序
[code]
str = "hello"
eval "str + ' Fred'"
[/code]

5, 用Proc定义代码块
[code]
pr = Proc.new { |x| puts "Called with argument #{x}" }
[/code]

6, 用lambda定义匿名方法
[code]
lam = lambda { puts "A lambda!" }
lam.call
[/code]