Ruby access magic | 易学教程

问题

Assume, I have the following class:

class MyClass
  attr_accessor :vars

  def initialize
    @vars = []
  end

  def add_var var
    @vars << var
  end

end

I want to access inners vars like this:

x = MyClass.new('root')
x.add_var 'test'
x.add_var 'something'
x.add_var Myclass.new('google')
x.google.add_var 'nice'

puts x.test
puts x.something
puts x.google.nice

Generally speaking, is it possible? What/where should I dig for?

回答1:

It's part of the standard Ruby library, and it's called OpenStruct:

#!/usr/bin/ruby1.8

require 'ostruct'

x = OpenStruct.new
x.google = OpenStruct.new
x.google.nice = 'Nice.  Real nice'
p x.google.nice        # "Nice.  Real nice"

You can also initialize attributes in the constructor:

x = OpenStruct.new(:google=>OpenStruct.new(:nice=>'Nice.  Real nice'))
p x.google.nice    # => "Nice.  Real nice"

回答2:

If you want to implement something like this yourself you should find out more about method_missing. This method gets called when a method cannot be found. Using some clever code to find the called method name in your @vars and react on that.

This is probably the same method used by the plugin weppos is talking about.

回答3:

Sure you can. This is exactly what, for instance, this plugin does for application-wide configuration settings.

回答4:

you can do this with instance_varibable_set and instance_variable_get:

MyClass.instance_variable_set(:@var_name, "value")

回答5:

Just dynamically define a new method and have it return the object you want:

class MyClass
    attr_accessor :vars
    attr_reader :name

    def initialize(name)
        @name = name
        @vars = []
    end

    def add_var(var)
        @vars << var

        if var.instance_of?(MyClass)
            class << self; self; end.send(:define_method, var.name.to_sym) {
                var
            }
        end
    end
end

x = MyClass.new(:x)
x.add_var MyClass.new(:google)
x.google.add_var MyClass.new(:nice)
x.google.nice.name #=> :nice

来源：https://stackoverflow.com/questions/2108986/ruby-access-magic

标签

ruby

singleton