Ruby classes and << Syntax

Ruby
1

I have written a simple snippet of code and would appreciate any help
with understanding what’s really going on.

Creating Basic Class

class Person # Same as: class Person < Object
attr_accessor :firstname
attr_accessor :lastname

def initialize(firstname, lastname)
@firstname, @lastname = firstname, lastname
end

def fullname
@firstname + ’ ’ + @lastname
end
end

Create two instances of class Person

john = Person.new(‘John’, ‘Doe’)
john.firstname # => “John”
john.lastname # => “Doe”
john.to_s # => “#Person:0x356678”

jack = Person.new(‘Jack’, ‘Stone’)
jack.firstname # => “Jack”
jack.lastname # => “Stone”
jack.to_s # => “#Person:0x3512f4”

class Person
def to_s
'Person: ’ + fullname
end
end

john.to_s # => “Person: John D.”
jack.to_s # => “Person: Jack Stone”

Everything as expected until here…

Now the interesing part:

class <<Person
def birthday
‘2008-05-16’
end
end

NOT EXPECTED:

john.birthday # => NoMethodError: undefined method birthday' for #<Person ...> jack.birthday # => NoMethodError: undefined methodbirthday’ for
#<Person …>

frank = Person.new(‘Frank’, ‘New’) # => Try with new instance
frank.birthday # => NoMethodError: undefined method `birthday’ for
#<Person …>

So basically my question is: What does the ‘class <<Person’

Statement really do?

Thank you very much!
Christoph S.

2

On Fri, May 16, 2008 at 11:54 AM, Christoph S.
[email protected] wrote:

@firstname, @lastname = firstname, lastname
john.lastname # => “Doe”
end
end
end

You are defining a class method and not a class instance method. Do
this…

class Person
def birthday
‘2008-05-16’
end
end

Todd

3

Which means:

class <<Person
def birthday
‘2008-05-16’
end
end

Is EXACTLY the same as:

class Person
def self.birthday
‘2008-05-16’
end
end

Or:

class Person
class <<self
def birthday
‘2008-05-16’
end
end
end

Thank you very much!
Christoph S.

4

Which means:

class <<Person
def birthday
‘2008-05-16’
end
end

Is EXACTLY the same as:

class Person
def self.birthday
‘2008-05-16’
end
end

Or:

class Person
class <<self
def birthday
‘2008-05-16’
end
end
end

True, but all 3 are class methods and none will work as you intend.

You would have to call Person.birthday to get a response and everyone
will have the same birthday (what a party!)
Of course you knew that, but some readers might not and I am bored, so
I wrote this.