Rails宝典之第六式: Symbol to Proc

这次来介绍ActiveSupport里对Symbol的扩展，我们先来看active_support/core_ext/symbol.rb文件:

class Symbol
  # Turns the symbol into a simple proc, which is especially useful for enumerations. Examples:
  #
  #   # The same as people.collect { |p| p.name }
  #   people.collect(&:name)
  #
  #   # The same as people.select { |p| p.manager? }.collect { |p| p.salary }
  #   people.select(&:manager?).collect(&:salary)
  def to_proc
    Proc.new { |*args| args.shift.__send__(self, *args) }
  end
end

原来&符号用在symbol前面实际上是调用了to_proc方法，而to_proc里返回一个Proc对象，内部为调用symbol指定的方法
结合例子来说，就是:

people.map { |p| p.name }
等价于
people.map(&:name)

即，&:name实际上调用了每个people对象的name方法，这样对对象的任意public方法我们都可以使用&+symbol来调用