类的实例方法

Question

I want to see what methods are unique to a class instance (class Pathname). I do:

Rails.root.class.methods(false)

And I get:

[:getwd, :pwd, :glob]

Then, I call one of the methods:

Rails.root.pwd

And I get:

NoMethodError (undefined method `pwd' for #<Pathname:/Users/borjagvo/workstation/npilookup>)

Why do I get this error? How can I see the public methods for instances of Pathname only?

Thanks!

Answer 1

You have to call class methods on class, like

Rails.root.class.pwd

OR

Pathname.pwd

For getting all instance methods (no ancestors nor singleton):

pry(main)> Rails.root.class.instance_methods(false) # OR Pathname.instance_methods(false)
=> [:write, :join, :+, :/, :as_json, :directory?, :exist?, :readable?,
    :readable_real?, :world_readable?, :writable?, :writable_real?, 
    :world_writable?, :executable?, :executable_real?, :file?, :size? .....]
# Then you can call above methods on instance of a Pathname
 pry(main)> Rails.root.size?
 => 1248

Answer 2

You are fetching the methods from the class of Rails.root , ie Pathname 's class methods:

Rails.root.class        #=> Pathname
Pathname.methods(false) #=> [:glob, :getwd, :pwd

To get the instance's methods, use:

Rails.root.methods
#=> [:mountpoint?, :root?, :each_filename, :descend, :ascend, :write, ...]

Or, to get its singleton methods: (there are none, it's an ordinary Pathname )

Rails.root.methods(false)
#=> []

Note that Rails.root is an instance of Pathname and already represents your app's working directory:

Rails.root
#=> #<Pathname:/Users/borjagvo/workstation/npilookup>